# Jet Jon Build Pics ...VIDEOS LINKED!!!!!!



## majkowskid (Jul 14, 2011)

So, with help from a couple of people i've met online, i've been in the process of converting a 13.5' Explorer fiberglass flat bottom boat into a 'jet-jon' utilizing the engine/jet pump from a 2000 yamaha xl700 ski. 

it's been slow going until recently, because of the mass amounts of fiberglass work i had to do. lots of cutting, sanding, glass, etc. 

I've never attempted anything like this before, and i must say i'm proud of myself! the boat was given to me, and the jet ski was wrecked and i've traded a bit of labor for it. The engine only had 51 hours on it, so it's in prime condition. 

I hate to say, i didn't have pics of the boat before i started working on it. didn't have a camera at the time. 

This is what it looked like as i was fiberglassing in the bottom portion of the jetski hull / jet intake and motor mount section. 







Finished fiberglass and applied 4 coats of Easypoxy marine bottom paint. used a 12$ spray gun from harbor freight tools.... this is before i put a clear coat on it. This is my first ever attempt at paint! Came out pretty good! 





Finally got a trailer and was able to flip the boat over and start on the interior. Engine mounted. 






Interior painted with Easypoxy topside paint gloss grey. PWC trailer tongue extended 4 foot, painted metallic black. 





Started interior flooring. 





That's how it sits as of today. very little budget for this. gotta save up some cash! 

stay tuned for further updates! planning on front deck, aluminum fuel cell, minn kota trolling motor up front, center console, etc.




UPDATE 9/27! 

99% DONE! just waiting on the fuel tank to come in the mail! throttle successfully installed yesterday, and works PERFECT. all electrical except for trolling motor wiring complete, key ignition installed, and console built. (console is not complete together in these pics. coverings are just laying in place. not secured down yet because of wiring to be completed)

runs GREAT. can't wait to get it on the water! hopefully next week!


----------



## fender66 (Jul 14, 2011)

This is the coolest looking motorized bathtub I've ever seen. :mrgreen:


----------



## Ranchero50 (Jul 14, 2011)

Majkowskid, looks good so far. 

You might have some air ingestion problems with those two big strakes but the ski hulls spoon might save you. 

Are you going to straddle the engine with the center console or try to stay in front of it?

Jamie


----------



## majkowskid (Jul 14, 2011)

Jamie, 

ya know, that's my biggest issue right now. i have NO idea whatsoever as to where to hook up the controls. 
i was thinking that i'd sit in front of the engine, but that pus me up really far in the boat. basically, i'm going to build a box around the engine that will be easily removable. i figured the front side of the box i could lean on and use for the seat back. but man, that puts me sitting WAY far up front! 

on the other hand, i could build the steering wheel assembly (how i do that i have no idea yet) into the BACK of the same box, and i'll be sitting behind the engine, on top of the prop driveshaft tunnel. but that may be too much weight in the back. 

i've got a custom gas tank on order that'll be going in the front of the boat, along with my optima blue top battery, and trolling motor, so that may weight down the front quite a bit, so sitting in the rear may be ok. 

i just didn't want to be sitting way up high in the boat..... i think i'm going to have to wait to plan the control center until after i get the flooring in and such, and i get a better idea of how much room i have to play with. 

what would you suggest?


----------



## Ranchero50 (Jul 14, 2011)

I would suggest reading my build thread. I tried to explain what I did and why I did stuff. Might help you make some decisions. 

The engine looks like it's right at the CG... Do you have any better pictures, say of the side profile and maybe some dimensions for the center of the engine? 

I still think straddling the engine may be your best best, think OCC chopper. Maybe make a flip forward console / engine cover / seat assy. Reusing the ski steering and throttle setup will save money on cables and probably the wiring too. If the fuel tank was behind the engine on the ski I would put it there on your hull too. Battery and troller up front should counter the fuel tank weight.

On mine I'm sitting right on the front of the engine. Front of the console is mid point on the hull and I straddle it with my knees. What's the endurance on the engine fuel wise? Mine will go through 9 gallons in 45 minutes at WOT but it's only a 5-6 minute run to my fishing area.


Jamie


----------



## majkowskid (Jul 14, 2011)

Jamie

Trust me I've read your entire build 100 times  if u remember I e mailed you a couple of months ago before I started this build. I would love to sit right where the engine is but I am afraid ill be sitting up too high. For such a small boat. Right now the top of the motor is about 3 to 4 inches higher that the sidewall of the boat. Boat is 48 inches wide by the way........as far as fuel goes its a 2 stroke and from what I've read it'll run wide open for about 1.5 hrs on a 13 gal tank....I'm having a 9 gal tank built 4 it. 

I plan on using the stock cables if possible but I've got to figure out how to adapt the steering cable to what I've got for a steering bow....I've got a steering shaft and gear box from a lawnmower id like to use.....for a throttle I've got a hot foot  

Lemme finish the floor and engine cover and ill see what it looks like for sitting in the engine box.....it may work out good!


----------



## Ranchero50 (Jul 14, 2011)

Sorry, the boat get's lots of fan mail. #-o 

My butt is about 4" above the gunnel, doesn't seem to be an issue and if anything it helps me see down into the water to avoid the nasties.

Jamie


----------



## majkowskid (Jul 14, 2011)

Hmmmm....you've just about got me convinced to sit on the engine.....ur boat just looks soooo much bigger than mine. Well I guess I can always change it later......marine carpet just got here on freight truck....time to finish up the floor!


----------



## semojetman (Jul 14, 2011)

I love the project, but I have to agree with fender66 I wouldn't be sure whether to put the water in it, or it in the water.


----------



## majkowskid (Jul 14, 2011)

wow, you guys are harsh! it's virtually the same thing as a 14/48 aluminum jon boat, just a bit squarer. it's an explorer brand boat, made for saltwater flats. 

hopefully when it's finished and rigged out for fishing, you guys will change your mind  

carpet just got here. it's corinthian charcoal grey marine carpet. i couldn't believe the difference in quality between the stuff at home depot or lowes and this stuff. has a rubber backing and is extremely flexible. should go nicely with the boat. 

within the next week or so i should have the front deck complete and the trolling motor mounted.... then it'll be time for the float test!


----------



## reedjj (Jul 14, 2011)

The motor looks like its right in the center of the boat? I like Ranchero's Idea of using a center console as a hood for the motor. 

You could put a deck on the back with some sort of fuel cell integrated into it running lengthwise down the center line. Maybe a bench seat mounted on it that flips up to access everything. 

I have no idea what im talking about! Just throwing ideas out there.

I wish I had the skills, imagination, equipment, and guts to try one of these builds!


----------



## majkowskid (Jul 14, 2011)

it's not exactly in the center... it's about a foot and a half more towards the rear. i think ranchero was actually talking about me physically sitting on what i build to cover the engine.... mount a seat on top of it basically, and making a small center console much like his to mount a foot or so in front of it.


----------



## Ranchero50 (Jul 14, 2011)

Sort of. I'm thinking straddle the engine from behind like a chopper with the low slung seat where the gas tank is about chest height, except instead of a gas tank you'll have a console and controls sitting on the engine. You are going to need to be tail heavy to run well so I don't you'll want to be forward of the engine, especially if you ever plan on taking someone along. 

BTW, you are overthinking your steering. There is no effort to turn the nozzle and I'm only about 90` lock to lock on the wheel.

Jamie


----------



## majkowskid (Jul 15, 2011)

jamie, 

i thought you meant to sit on top of it... i'd LOVE to sit behind it, but i think it's a bit too large to straddle  i'd be sitting like i was riding a horse... a BIG horse... or at least i think i would... have to do some measuring this weekend.


----------



## benjineer (Jul 15, 2011)

I say sit/stand behind the engine too. You may have to build the floor up a little to have it be flat in that area. You want to be in the back if you hit waves/chop. Since you are talking about flats boats, take a look at some pics of them. The console is always close to the back even on long boats. The front bounces up and down on the waves, and the back is where the most comfortable ride is.


----------



## Ranchero50 (Jul 15, 2011)

I think it'll work. Put a mid height casting deck 4" below the gunnel that ends at the back of the engine mount the steering setup from the ski at the front edge of the engine. My console is 18' wide, no drama.

Throw a stool in the boat, sit on it and make some motor noises. Helped me considerably. 
Jamie


----------



## majkowskid (Jul 20, 2011)

got the flooring completed and carpeted. battery box mounted in front of engine. Next step is to build the console/engine/battery box cover. 







finally got the cooling lines figured out. the pisser exiting the back of the boat (hanging in pic) will be removed. there will be 2 pissers exiting the top of the transom directly above the jet. hopefully front deck will be completed this weekend and i'll be able to float test it with the trolling motor!


----------



## bulldog (Jul 20, 2011)

Looks great. Keep up the good work and keep the pics coming!!


----------



## majkowskid (Jul 25, 2011)

update 7/25/11 

Got the deck extended up in the front 11 inches. new hatch in place. trolling motor mounted. 
there's now storage both in the front white hatch, and right behind it. planned on putting the fuel cell in the seat area that i built up front, but that's not going to work. i float tested the boat this weekend (no leaks! yay!) and there was far too much weight up front with me sitting there, and the 60 lb battery. 

i placed the battery and weight in the back, and it floated much better, so i'm going to locate the fuel cell to the rear with the battery. 

here's a pic of the deck finished, exhaust mounted, another drain plug in place, and all new cooling lines.


----------



## majkowskid (Aug 8, 2011)

got visual pisser installed left side of boat. rear deck almost complete. seats coming in the mail. this pic doesn't show it, but i got the bow and stern lights mounted and electrical ran. horn mounted on bow. electrical parts coming in mail from a buddy. another drain plug installed. 

nearing completion! hopefully this weekend seats should be in, engine cover built, and steering built. perhaps i'm too optimistic.


----------



## bulldog (Aug 8, 2011)

Looking great so far. Clean and professional. Keep up the good work.


----------



## majkowskid (Sep 27, 2011)

UPDATE 9/27! 

99% DONE! just waiting on the fuel tank to come in the mail! throttle successfully installed yesterday, and works PERFECT. all electrical except for trolling motor wiring complete, key ignition installed, and console built. (console is not complete together in these pics. coverings are just laying in place. not secured down yet because of wiring to be completed)

runs GREAT. can't wait to get it on the water! hopefully next week!


----------



## PSG-1 (Sep 27, 2011)

It's looking good! You should be able to access some narrow and shallow areas with a boat that size!


----------



## Billvsthefish (Sep 28, 2011)

Thats a sharp looking boat you got there. I also like your seating arrangements. Its gonna be lots of fun.


----------



## fender66 (Sep 28, 2011)

Turned out great. Love to see some video of it running. :wink:


----------



## majkowskid (Sep 28, 2011)

once i get the fuel tank in, i'll be sure to take a video of it on the water


----------



## majkowskid (Sep 29, 2011)

man, what a pain in the butt getting this thing registered in texas! 

had to transfer the boat title into my name... fine. i understand. 
had to transfer JETSKI that engine came out of into my name, even though jetski is destroyed... ok, kinda understand. 
had to then fill out affadavit for jetski being destroyed. then, when new title gets to me in my name, i have to surrender it to the TPWD. wtf? 
then, i had to pay for a NEW title, utilizing the old boat's HIN, but showing that it's a homebuilt boat. shows "inboard" powered now. 

total cost = 1 ARM 1 LEG. 

rediculous.

that being said, the TPWD guys are awesome. really nice. front desk clerk called out a couple wardens and a lake patrol guy to look at my creation. 
Lake patrol officer wants to "run me" in their lake boat, which is a 18 foot center console with a 150 hp outboard. he says it'll run 42 mph supposedly. hmmm... wouldn't it be nice to smoke the lake patrol in a 13' jon boat???


----------



## fender66 (Sep 29, 2011)

> Lake patrol officer wants to "run me" in their lake boat, which is a 18 foot center console with a 150 hp outboard. he says it'll run 42 mph supposedly. hmmm... wouldn't it be nice to smoke the lake patrol in a 13' jon boat???



Never happens if we don't have a video to watch. :LOL2:


----------



## PSG-1 (Sep 29, 2011)

Sounds almost like my fiasco with the Aluma-Jet.

The story behind my boat goes back a ways. Before I acquired it, someone had brought it to me to give them a price to fix the extensive corrosion on the bottom. I told them it would be in excess of 500 dollars, and they balked at the price. 

At some point, they traded it in to a marine dealer when they got a new boat. Some time after that, the marine dealer took it to another welder, wanting a price to fix the corrosion. He told them about the same thing I told them....roughly 8 hours of labor at 75 dollars an hour. So, once again, it was put in storage.

A few years later, that marine dealer went out of business, and they pretty much gave the boat to the other welder, who had done a lot of work for them in the past.

A couple more years passed, and the other welder went out of business, and moved all of his equipment out to his property where he lived. Not long after that, he was selling that property, so, he had to get rid of a lot of the stuff he had stored out there, and I went out there to see what I could buy.

I came home with a good assortment of aluminum and stainless, as well as paying 50 dollars for that DuraCraft. I initially planned to cut all the ribs out of it, and anything else I could use for repairing other boats.

But, as I looked at it, I saw that the corrosion was primarily on the center V, and I knew I could fix it, so I did.

Well, I ran into an issue when I went to title it. When I bought it, I was told that it had no title, but since I planned to use it for scrap, I didn't really need one. The hull ID tag had been removed. So, I had to contact SCDNR. I sent them photos of the boat, and told them what I had done. They sent a marine investigator out to see what he could determine. He came out, and found the alternate hull ID number (boats always have 2) He wrote me and the seller a warning ticket for selling/purchasing a watercraft without a title. He said because I had not tried to turn around and sell the boat for profit, that it would just be a warning ticket. He said that he would run the number, and as long as it wasn't stolen, they could issue a title for it.

It took a couple of months, but they were able to re-issue the title, even with the same registration numbers (I guess the same registration number stays with the hull as long as it's in the same state)

So, long story short, I got it titled. Although I filled out the paperwork and listed it as an inboard engine with jet propulsion, my registration still lists it as an outboard. LOL


Not sure about being able to outrun the game wardens' boats.....but I can tell you that game wardens have been aboard my boat several times, when I have taken them out on the water to write tickets to natural resource violators that I have witnessed, such as illegal duck hunting within the state park, poachers robbing crab pots, people harvesting shellfish from polluted areas, or at night, and numerous other violations. There's probably been at least 200 tickets/cases made from aboard that boat.

They pretty much understand that I know the creeks around here better than they do, especially at low tide, and that my boat can get into areas that their patrol boats can not. The guys in SCDNR do a helluva job, but they also cannot be everywhere at once. Concerned, observant citizens are the bulwark of a conservation officer's arsenal of resources in the fight against violators.


----------



## Anonymous (Sep 30, 2011)

majkowskid, where is this rig going to be fishing out of?



PSG-1 said:


> It's looking good! You should be able to access some narrow and shallow areas with a boat that size!


----------



## majkowskid (Sep 30, 2011)

we have 2 local lakes. one is dang near dry, but there's some nice areas left that are too shallow for props. the other lake is small and is basically kept at a constant level. (by draining the other lake!) it's got some nice inlets and such as well i'd like to sneak around in. why do you ask?


----------



## majkowskid (Oct 11, 2011)

TODAY WAS THE FIRST TEST RUN! 

I need some help though to all whom have built one of these. please look at my pics in my first post to reference bottom of boat. 

i'm having MAJOR cavitation issues. like BIG TIME. 

on perfectly flat water, i hit 41 mph via gps. if there is ANY waves, it starts sucking air majorly. water has to be like glass for it not to happen. 

i'm thinking its mostly from the ribs that are on the bottom of the boat. these are structurely important as the boat hull is thin, but i'm wondering if i can cut "gills" into it to help direct water from outside the ribs to inside them... besides that i don't know what to try. i already have the spoon idea going, but i'm guessing i didn't construct it the right way. i seriously think 99% of it is from the ribs though. 

if anyone has any suggestions (ranchero50) i'd appreciate it! someone told me about an intake grate that has a scoop built into it that would probably help... worth a shot??


----------



## Ranchero50 (Oct 12, 2011)

I think you are screwed... :shock: 

How about a picture showing you sitting on it in the water, maybe a couple decent pictures from the side without the background blotted out so we can have some perspective.

As a guess I think your intake is too far forward for the length of hull, you are sitting too far aft and at higher speeds in chop even the spoon is coming out of the water as the hull planes on the ride plate under the nozzle. Only real fix is more weight forward to keep the nose down. Again, some pics or video of it in action will help troubleshoot or eliminate a lot of variables.

Mine will cavitate in too heavy chop as well but I don't run it that hard because of the hull pounding.

Jamie


----------



## majkowskid (Oct 12, 2011)

Ranchero. 

Thanks a lot for the response! 

We took a video on my buddy's phone and we're working on getting it uploaded. 

I'm pretty sure that it's not a weight issue. It actually ran BETTER with only two people in the boat, than with a third sitting up front. (37 mph with 3 people in it, but it had to be STILL water). 

what's funny is that it actually runs better with the nose sticking up out of the water (before it planes up) than it does on plane in any type of chop. 

do you not think it could be from the ribs on the bottom of the boat that are in this pic? 
or is my spoon area not right?






this is what i was trying to explain about cutting some slits in the ribs to direct water to the pump... also thought maybe one of the higher end intake grates with the scoop on it may help keep the pump loaded?


----------



## majkowskid (Oct 12, 2011)

oh, and sorry about the pics.... i will update with some more. i built the boat in my buddy's garage (he had more room at the time) and he didn't want pictures of all stuff all over the internet, so he made my blot them out. 


i'll take some pictures either today or tomorrow showing the complete profile. the intake is actually WAY far back on the boat. i'm not too sure about the theory about the pump sticking out of the water... as i said above, when it's and 1/4 throttle, before it planes up, it actually doesn't cavitate at all. even on glass water... and i mean GLASS it still cavitates a bit. it's almost like the "tunnel" area created by the ribs is keeping any water from the sides from being sucked into the grate.


----------



## lovedr79 (Oct 12, 2011)

Have u thought about a top loader grate and an extended ride plate? Possibly change the impellar to a different pitch


----------



## majkowskid (Oct 12, 2011)

lookin into the intake grate as we speak... impeller i didn't think of. what's the purpose of the ride plate? how would that affect the intake?


----------



## Ranchero50 (Oct 12, 2011)

That you've gotten it to go over 20mph is more than most guys get. That it runs up to 40mph on flat calm says the pump is staying loaded (everything is working) at that speed so I don't think a load grate will help much but if you find one cheap it can't hurt to try it out. Load grates work by forcing the water around the curve of the inlet roof when the hull is going to fast for the water to naturally bend without cavitating along the roof. At 40 you aren't that fast. 

That you are cavitating at speed in chop tells me that your pump isn't drawing air free water in that chop (seems basic enough right?) so I would try to get the hull to draw air free water vs. just more water. 

Cutting the strakes as drawn I don't think will do anything except make it worse. If anything I would look at cuttng them the other way to allow air to escape from the centerline. What concerns me is I don't know what will happen to the water under the center of the hull at speed if it's being vented out the side with the air. Possibly less pressure causing more cavitation, possibly more more planing effect on the outer section of the hull.

I think what you can do that will make the most effect is lower the middle of the spoon so it draws from deeper, less aerated water. My spoon draws @ 1.5" deeper than the strakes run, in chop I have to get the kid to lean over the bow to minimise the cavitation. Simplest test would be screw on a couple 4" wide sections of luan (5mm plywood) to get a profile and then body putty over them and play with it.

Now that it's together you get to make it run right. Kind of why mine still isn't finished 
Jamie


----------



## PSG-1 (Oct 12, 2011)

lovedr79 said:


> Have u thought about a top loader grate and an extended ride plate? Possibly change the impellar to a different pitch




Good suggestion. I was about to suggest the same thing. A top loader grate will feed more water to the pump, to keep it from starving out and cavitating, even at 40 MPH. 

Shifting more weight to the rear will also help, it will sink the pump a little lower in the water, but you may need trim tabs to offset and prevent porpoising. He did say that it ran better without a person in the bow, with the bow being up some, so that tells me that putting weight on the stern, theoretically, should work.

Also, try a "Concord" or 'swirl' impeller, rather than a straight rake profile. The swirl impellers are a little more forgiving of cavitation. 

If you're running a progressive pitch impeller, such as a 13/19, you may even need to have the pitch modified, maybe to something like a 14/16. Again, this is one of those variables that you have to experiment with.


----------



## Billvsthefish (Oct 12, 2011)

I've been following your build. I think you need a more defined spoon. With a flattie, air and water go straight back. I think you need something to disperse the air, or redirect it rather. I had your same problem, and i built a spoon (Ranchero's idea). It took away 99% of my cavitaion. But i do have an aftermarket intake and ride plate, but even with these i still had cavitation. Take a look at my spoon, it definately works. Bill
https://www.tinboats.net/forum/viewtopic.php?f=21&t=21899


----------



## PSG-1 (Oct 12, 2011)

majkowskid said:


> do you not think it could be from the ribs on the bottom of the boat that are in this pic?
> or is my spoon area not right?



No, but looking at the pictures, it appears that you have a 'step' between the hull and the body of the pump intake, it appears the pump intake is not flush with the hull, like it may be inset by a half inch or so. (Correct me if I'm wrong, and if I'm wrong, then, ignore the next part)

This step could be part of your problem, it will cause turbulence, right before the intake, which is something you do not want to do.

You could try to fill this void somehow, and try to blend and taper it, but the pump is still going to be inset from the hull, so, I don't think that will eliminate the problem.

Hate to say it, but it looks like the best option is to try to drop the pump a little bit, to get it flush with the bottom of the hull. Unfortunately, this may also mean having to change your motor mount design, to also drop the engine lower, to keep in line with the pump when you lower it. I know that isn't what you want to hear, but IMHO, I think that's the best course of action.







this is what i was trying to explain about cutting some slits in the ribs to direct water to the pump... also thought maybe one of the higher end intake grates with the scoop on it may help keep the pump loaded?



[/quote]


A top loader grate. Instead of having numerous longitudinal tines, most top loaders have 2 scoops on them, and they are supported by one massive tine on either side.

I ran a top loader on the Aluma-Jet for a while, but the problem with it, is when you operate in areas where there are weeds, etc. As it doesn't have a 'grate' so to speak, it becomes an even bigger vacuum cleaner, sucking up everything in its path.

When I designed the weedless grate on my boat, I really wanted to keep the top loader grate, but it was logistically and mechanically impossible to have a top loader grate AND a conventional grate with longitudinal tines operated by a push pull cable on a pivot..... so I had to choose between being able to operate in heavier chop without cavitation and not having a way to clear a fouled intake grate, or being able to clear my grate, but being more limited to operating at slower speeds in chop. In the end, I went with my weedless grate.

One other thought I had was that the sharp "V" in the hull ahead of the intake COULD be causing some turbulence, but before you try to modify that part of the hull, I would suspect that step between the pump and the hull.


----------



## Ranchero50 (Oct 12, 2011)

Bills build was the one I was thinking of when I mentioned the plywood built up. The step that PSG mentioned is where better pictures could save the day.

I'm in the same boat with the grate, I like being able to glide over the weed beds but have to go slower in chop vs. sucking up everything in the water. I'm sure I'll be sucking up leaves in a week or so.

Jamie


----------



## PSG-1 (Oct 12, 2011)

Yeah, the cypress trees are starting to drop some of their foliage in the rivers and swamps around here. Even with the weedless system, when I came back from a trip to the Waccamaw River last week, I found a wad of leaves on my intake grate, and another small wad wrapped around the push-pull cable that controls the weedless grate. Even so, it didn't cavitate much, which surprised me. Heck, it surprised me that I had a wad of leaves under there, as I did activate the grate a couple of times when I was in the river.

Another thing I suggest for those who run in debris-filled water....get yourself a "Shurflo" inline water filter, with 1/2" barb fittings, and plumb it in between the pump and the engine. It has a removable cap, and a strainer screen that will prevent trash from clogging your water passages in your engine.

One other thing I would suggest, and I went ahead and put one on my boat.....get a teleflex water pressure guage (they are 2" in diameter, like most fuel, temp, voltage guages) it reads from 0-35 PSI. You will have to run a small diameter hose (very similar to speedometer hose) from your console back to the engine compartment. 

Plumb the T fitting in AFTER the water filter, not before. If you put it inline before the filter, if the filter becomes clogged, the guage will still read water pressure. If you put it after the filter, then, if the filter clogs, it will show a drop in water PSI readings, and you IMMEDIATELY know that there is a problem, you're not having to constantly watch indicator stream fittings to see if they're peeing, etc. Simply glance at the guage, and it will tell you in an instant.


----------



## majkowskid (Oct 13, 2011)

thanks for the help guys! i've got a couple things i want to try, but it may have to wait a little while. i think first thing will be an intake grate. always a good upgrade anyways. 

as far as the "step" you speak of, are you referring to the left and right sides of the intake grate as shown in the pic above?? (btw, i'll have pics this weekend sometime... my camera wouldn't work yesterday so i'll have to borrow one) 

if that's what you're referring to, i may be able to alleviate that this winter... i can potentially fill that void and fiberglass over it, but it's gonna be a pain in the rear now that i can't flip the boat!


----------



## majkowskid (Oct 13, 2011)

Ranchero / PSG. I found a little better picture of the bottom... still dont have a camera yet. this was before it was painted. 





the circled areas are what i think are causing the problem now. i did a bit of research on the purpose of a spoon on a jet boat, and now i understand what you're talking about. 

here's my idea /thinking:

i can taper the large circled area (which sticks down quite a bit from the flat portion of the boat) by creating a template out of carving foam, and tapering it towards the front of the boat 2-3 feet. i can fiberglass this on to the bottom of the boat. 
the two smaller circled areas are little "pockets". i rushed this area of the fabrication, and i admit that. i know they need to be smoothed out. 

do you think this would help? i would think that the natural "spoon" that is built into the jetski hull that i attached to the boat should suffice for what it needs. i'm really thinking that the large circled area is just diverting water from hitting the pump because of the turbulance caused by it.


----------



## PSG-1 (Oct 13, 2011)

Yes, that's the area I was referring to (your last photo with the circled areas) In the pics with the pump installed, that area appears to be stepped up from the pump. Also, those areas you have circled could cause turbulence, but if you have the pump flush with the bottom of the boat, it wouldn't be as severe. That step in the transition between the hull and the body of the pump, combined with the peak and valleys that you show in the circled area....would definitely be the primary suspect for cavitation. The longitudinal strakes to the outside of the pump would cause turbulence behind the strakes, as well as on the leading edge, but that is not in front of the pump intake, so it would have no effect on the pump's performance.


----------



## majkowskid (Oct 13, 2011)

yeah, the more i think about it that's probably a lot of the problem. here's a quick drawing of what the boat technically looks like from the side view, but exaggerated a lot.





i'm thinking i can profile it down this winter and create a gradual slope under the boat, and integrate a spoon like jamie's. i think you guys are right... the ribs probably aren't affecting it as much as i think. i think that big bump is pushing the water clear of the pump.


----------



## PSG-1 (Oct 13, 2011)

For all visual purposes, the area you have shown in red indicates the location and shape of the air pocket that is forming as the boat moves across the water. This is most likely the source of the majority of your cavitation.

The area that I was initially referring to, is on the BACK end of that hump, where your pump bolts into the hull. From previous photos, it looked like there was a step in the transition between hull and pump, like the pump may be inset from flush with the hull by about 1/2" or so. If that's so, then, that step could also cause some issues with cavitation.

But after seeing the drawing you did, I would also tend to agree with your assessment about that step on the front side of the hump causing the problem. That is a pretty large step, and if it does not transition in some type of smooth taper, it will definitely create an air pocket, a large one in fact, likely enough to cause it to cavitate. It's not cavitating on flat water because the hull is flat out, and has displaced the air from underneath, and will continue to run as such until you hit some chop, which allows air to get between the hull and the water. With a flat bottom or a spoon, this isn't an issue, as the air is displaced or dissipated by the time it reaches the pump. But if you have something on the hull that breaks up the smooth transition of the water, the air is going to collect at this point, and 'bleed off" toward the pump intake, causing it to suck up the air and cavitate.


----------



## majkowskid (Oct 13, 2011)

good to have affirmation of what i'm thinking. it's actually a bit more complicated because there's some weird angles going on from the jet ski hull portion, but i'm going to get it all rounded out. i'm sure it'll take some time espescially working on my back under the boat. i'm not about to disassemble the entire thing to do this  block and tackel, raise it up a bit off the trailer, and do it from underneath.


----------



## majkowskid (Oct 13, 2011)

got two videos posted! well, my buddy posted them on facebook, and i can't download them!

working on it!


----------



## Ranchero50 (Oct 13, 2011)

Can't do Fbook...


----------



## majkowskid (Oct 13, 2011)

dang it... doesn't work. i have to get my buddy to upload them to another site. gimme a little while 

ranchero / psg, here's a quick pic looking from the FRONT of the boat, down the bottom. you can see that the intake grate is about 1 inch BELOW the actual bottom of the boat... but you can also see the terrible hump that i'm talking about.


----------



## PSG-1 (Oct 13, 2011)

Oh, OK, yes, that shows it in better perspective. That helped clarify it for me. 

Now I see that the pump IS flush with the hull. I guess some of the other photos were playing tricks on my eyes, there appeared to be some type of anomaly between the hull and the pump, I guess it was just a shadow.

Seeing the hull from this angle, I would say yes, definitely that sharp V is causing the issue with turbulence.

About the only way to fix that is by doing some glasswork, making it transition from the hump, down to nothing where it meets the hull forward of the pump, smoothing out the profile of that V and blending it to the hull.

If you do this, I can almost guarantee that the problem will be solved, as this stepped area definitely sits lower than the rest of the hull, keeping the pump hooked up won't be a problem, you might not even need the top loader grate after all .... with the pump being that low.

But again, that V is the most likely culprit at this point, as everything else appears to be correct.

You could experiment and find out for sure if this is the problem, perhaps forming up a small piece of plywood, and just scab it to the hull around its perimeter with a little cloth and resin, do a test run, and see if that fixes it.

If it does, you can easily snatch that 'band-aid' off the hull, and go ahead with your full modification like you mentioned earlier. 

And if it doesn't, you are able to find out quickly, without having to put a lot of labor into modifying the hull, and there being the possibility of it not working (but I have confidence that it WILL work)

In either case, a quick expedient patch that covers the void to do a test run is probably your best bet at this point. When you get into trial and error like this, you want to experiment with modifications that require the LEAST amount of time, material and labor. that way, if and when a mod doesn't work, you haven't invested a lot of time into it.


----------



## Ride_Klein (Oct 14, 2011)

Sorry to hear about your cavitation problems. Wish I was farther along with my project so I could offer you some real world advice. I do appreciate you documenting it so that those of us working on similar projects can hopefully learn. 

Congratulations on the top speed. I'm sure it felt great to scoot along like that.


----------



## Billvsthefish (Oct 14, 2011)

Looking at your last picture, i think the your spoon isn't big enough or shaped quite right. Right in front of the intake, needs to be the focal point of the spoon. It should be ramped, not flush or slightly "V-ed". This forces the water to keep the pump loaded.
Take a look at this: https://www.tinboats.net/forum/viewtopic.php?f=21&t=8385&start=105
The idea is to divert air to the sides of the intake (front of the spoon) and water to follow from the halfway point or just before that, along the curve of the spoon and up the ramp (rear of spoon). The spoon being curved side to side and front to back. Mine is kinda crude, Ranchero's being professional grade. But they work.


----------



## Ranchero50 (Oct 14, 2011)

My 2 cents is still that you need your spoon deeper so it's drawing from undisturbed water. I can't see my intake from the front. You want the spoon to push the aerated water out of the way and draw from the clean water.
















Jamie


----------



## majkowskid (Oct 14, 2011)

thanks for all the input guys! definately know what i need to do now... basically redesign the entire bottom of the boat between the ribs  i'll get it done, but it's going to be a while before i can get started. unless someone wants to donate a bunch of resin to me.....


----------



## majkowskid (Oct 14, 2011)

videos...you don't have to have a facebook acct to see them!

https://www.facebook.com/home.php#!/video/video.php?v=2245966422186

https://www.facebook.com/#!/video/video.php?v=2245960382035


----------



## PSG-1 (Oct 14, 2011)

On my boat, I didn't build any type of spoon.




You can see the center strake of the boat in this photo, before the jet unit was installed. I ran it with this center strake for a year or so, and in conjunction with the top loader grate, there wasn't much of an issue with cavitation.

But when I went back to a conventional grate and modified it to be a pivoting weedless grate, the cavitation showed up again. So, what I did was to take my sawzall, lay the blade sideways, and cut about 3 feet of that strake off the boat, taking it down flush to the hull in that area forward of the pump. Then, to cap it off, I used a piece of 1/4" plate, cut to the necessary width and length to cover up the void, then welded it to the hull, leak tested, and sealed with paint. (I don't have a pic of it right now, I'll try to remember to take one today)

My boat runs pretty good without the spoon, perhaps it would have better hook-up in choppy water if I HAD built a spoon in the hull, I'm not sure.

One option we discussed doing on the next build is a 'dropped hull' Basically, cutting out the hull and modifying it to be dropped lower than the rest of the hull by about 2 inches, setting the engine and pump as low as possible. From the transom end, the drop hull would appear to be a 'V' with the point flattened out...about as wide as the pump/engine area, then tapering down to nothing toward the forward end.

We figure setting the pump lower than the rest of the hull ought to allow for running in the snottiest conditions possible, with no cavitation.


----------



## majkowskid (Oct 14, 2011)

hmmm....

that's really weird psg... so basically you have a similar hump in front of your intake, and didn't have the issues. only difference is your intake grate. 

i really think i'm going to try that first... just get a top loader grate. i'd rather try a bolt on accessory before i go and start glassing. i figure it's a good upgrade to the boat anyways.


----------



## Ride_Klein (Oct 14, 2011)

Video helps. 

You mentioned in an earlier post that it ran better without weight up front. Were you referring to top speed or was your cavitation problem worse with the added weight up front? 

Looks like you might have a small problem with porpoising as well. (Boat wanting to bounce up and down on plane in pretty smooth water) Was this simply from hitting your own rollers, or does the boat bounce as you approach top speed? If it does porpoise, that isn't helping your cavitation problem any. You can remedy porpoising a couple of ways. The easiest is to simply add more weight up front. Use something you can move easily while running and see if that fixes your problem. Of course this solution is pretty useless if more weight up front makes your cavitation problem worse. 

Other solutions for porpoising include trim tabs or adding wedges to the hull.

Example of wedges.
https://www.duckboats.net/cgi-bin/forum/gforum.cgi?post=27369

You can test wedges pretty easily using a piece of wood that's taped to your hull with duct tape. This lets you try a couple different degrees and sizes of wedges to see if they help before you do any major work. 

You should be able to use the same technique to test any spoon modifications. Get some shape-able foam blocks from a craft store and mold/cut them to your desired shape. Tape 'em on there and hit the water. You can test a couple different setups this way without having to permanently modify anything on the boat. They won't hold on all day, but when they let go they're easy to find.


----------



## majkowskid (Oct 14, 2011)

it does porpous just a little bit when i'm the only person in the boat. with a friend up front, it's completely gone. i think once i get another battery up front for the trolling motor this will be completely eliminated. 

i was thinking about trying out spoons like you said, but would tape really hold at all? i would doubt it. trim tabs are an option for the porpousing as well....


----------



## Ride_Klein (Oct 14, 2011)

The tape won't hold it all day, but it will hold it much longer than you'd think. I've used it in the past to test wedges, flotation pods, and adding hook to an old ski boat hull help flatten out a nasty bump in the wake at 28' off. 

The trick is making sure you get the hull completely dry before you tape things on. This is much easier to do in the shop, but with enough towels you can get it done on the trailer as well.


----------



## PSG-1 (Oct 14, 2011)

majkowskid said:


> hmmm....
> 
> that's really weird psg... so basically you have a similar hump in front of your intake, and didn't have the issues. only difference is your intake grate.
> 
> i really think i'm going to try that first... just get a top loader grate. i'd rather try a bolt on accessory before i go and start glassing. i figure it's a good upgrade to the boat anyways.




Well, I never said I didn't have any issues with cavitation, because it will cavitate if you try to take a curve at too high of a speed, and it will cavitate when you get in chop that's more than 6 inches in height. But in light wind chop, and under most average conditions, no problems.

I had less cavitation with my top loader grate, for sure. But again, I wanted a weedless system, so, I had to trade off one advantage for the other.

BTW, here's the modification I made to the center strake:



OK, maybe not exactly flush cut, but definitely flattening out the V for a couple of feet like I mentioned.




Ideally, and on the next build I know to do this.....take out the ENTIRE center V of the boat, and weld a piece of 1/4 x 2" or 1/4 x 3" flat bar along the entire length of the cutout. I didn't do it on this one, because the boat was already built, and once you get forward of the engine compartment, there is foam in the hull, I didn't want to burn it up with the process of welding, and I figured at least by reducing the V for the length that I did would have an effect. And it does. 

Taking out the V and using 1/4 plate, removes the center V, but still gives a lot of structural integrity by using a piece of material that's twice the thickness of the hull itself.


----------



## mmf (Oct 15, 2011)

I LOVE your videos! Very comical too!! I like the REDNECKIN especially! Keep up the good work!!


----------



## PSG-1 (Oct 15, 2011)

mmf said:


> I LOVE your videos! Very comical too!! I like the REDNECKIN especially! Keep up the good work!!





By 'redneckin' I assume you're referring to the clip of me and Larry The Cable Guy out harvesting oysters? Yeah, that was some funny stuff! It took him about 45 minutes to get out of the mud, and his camera guy was buried even worse, it took 3 of us to get him out.


----------



## majkowskid (Oct 19, 2011)

well, i bit the bullet and ordered an intake grate for the boat. should be here monday. it's used, but in great shape, and it should fit my ski (it's hard to find accessories for an xl700 yamaha hull!) plus it was next to nothing in price. 


i want to see if that helps at all first. next thing i'm going to do is get some sponsoons for the side of the boat to help in the turns. 

i'll keep you guys updated.


----------

