# 14' Polar Kraft Jet Project



## Flat_Bottum (Feb 24, 2015)

Hello everyone, I just joined the site this evening. I have read a lot of threads from this site and since I am starting a project, I would like to share it. I built my boat almost 2 years ago but due to moving situations and life in general, it had to sit right after its 3rd shake down run and neighbors cars, wind and the most sap shedding trees I have ever seen in my life...the boat was ruined. So, I have just ripped out everything except for the engine and pump and I would like to share the new and improved build up of my boat for those who may be interested. The boat is a 1978 Polar Kraft flat bottom (not sure of exact model) and the power plant is a 1994 Polaris SL 750 3 cylinder triple carb. The ski came on a trailer my buddy bought for his stand up skis and it never ran right so he dumped it in his pasture and left it for a couple years. When I busted my outboard, I picked the ski up to build my own jet jon boat. Turned out, the stator wiring was fried so after a new to me stator from ebay, the engine runs flawlessly. Anyways, I am planning on revamping the boats interior from wood and carpet to full aluminum to completely get away from the rot factor. Here are a couple small clips of the boat at its maiden voyage after the build. 

First start up after the interior was complete, hadn't hit water at this point:




Here is the first start up and plane (sorry its short)




And a little romping. Sorry for the poor filming, it was my first time running a jet propelled anything and trying to drive and film at the same time is tricky. The boat died at the end because I had the carbs adjusted for a single feed inlet when I have a single feed line now going to each carb so under light throttle, it wanted to load up and die if I hit the throttle too hard. GPS said 44 mph was the top speed that outing.




And the day that it all began:


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## Brine (Feb 24, 2015)

Welcome to the site - Nice find on the ski 8)


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## Flat_Bottum (Feb 24, 2015)

Thank you. I have posted some questions on another PWC website regarding questions I have for this engine such as carb tuning with a triple outlet fuel pump, feed and return fuel pressures and pros and cons of using an electric pump over the stock mechanical. The engine runs great and has really good power to it for what Im using it for. I got the boat now to an almost bare hull and should be able to start framing in the next couple of days. I will post photos of my progress and welcome any and all advise or input since this is my first time framing in a boat this way.


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## Flat_Bottum (Feb 25, 2015)

I have spent the last few hours reading through peoples build threads here and was wondering why exactly do you put foam under your floor? I will be leveling my floor with aluminum angle and laying 1/8" aluminum sheet as my floor. I was not planning on adding any foam and never really thought about doing so. Is it for sound?


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## swlamarshrunner (Feb 25, 2015)

I believe they use it for floatation in case it were to try and sink or flip


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## swlamarshrunner (Feb 25, 2015)

Nice build by the way. Is 44mph the fastest you have seen out of it?


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## Flat_Bottum (Feb 28, 2015)

the first run net me 44mph but it was cavitating fairly bad in the chop. I modded the factory grate (have a second OEM grate just in case) with a small scoop on the very rear and it dropped me down to 41-43mph but hooked up much much better. 

Got some work done on it these past few days. Progress slowed considerably when I smashed a finger...hard to rivet one handed haha. Here are a few progress photos.

Stripped the hull and removed last remaining bench.







Got my fuel cell lined up and mounted.







Began installing floor supports and front deck framing. All angle is 1.25x.125" aluminum. Floor supports are 3/4x1.5" aluminum tube (where seen).













Added an electric sending unit to my fuel cell as well as a side mounted fill. Its a 1.5" stainless through hull fittings that I epoxied in. I will loose about 2 gallons worth of capacity but its a 16 gallon cell so I will be ok.


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## PA Delaware Fisher (Feb 28, 2015)

That's gonna be a fun toy when your done.


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## Flat_Bottum (Feb 28, 2015)

I have had it on the water 3 times since the first build and it was a blast! Not good at jet running as of yet so I hit lots of bushes and tree limbs but Im getting better. 

I do have a question though: The boats transom is low and I get a lot of splash back from the jet and I want to get rid of that. I was thinking of building some sort of small platform to cover the jet and linkages going out the back but not only do I not know what those things are called but would like to know if there is a certain way/type/style to build. If I spin the boat around and stay off the throttle I will get a wave over the rear side, cant really help that since the boat cant get any deeper and now without the fuel tank in the rear also, weigh should be better distributed. I would just like to get rid of the splash back from the rear. Any suggestions??


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## Flat_Bottum (Feb 28, 2015)

Also, I will not be using any carpet in this boat and would like to know what sort of paint are you guys using for your carpetless decks and floors that provides good life from peeling or scrapes? I dont want a paint that is going to come up just by sliding a tackle box across it or something.


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## Flat_Bottum (Mar 1, 2015)

So after much much much deliberation tonight, I have decided to rip the engine out of the boat along with the ski hull and completely redo everything. I initially used a lock tight epoxy to seal the ski hull to the boats hull then used the stupid foam to fill the gaps. However, I used that same epoxy to seal the pump housing to the boats hull and to seal some holes in the side of the boat when I mounted the first decking and when ripping the decking off, the lock tight stuff just pealed away and where I used 5200 (I learned about 5200/4000 later on in the game) I had to use flat head screw driver to pry off the boat. Bottom line is that if I am going through the trouble to revamp this boat and spending the money I have these past few days to do it then I might as well take the extra few days to rip it down and start all over. The hard part is done and I already have to holes and ski cut so pulling it out, wire wheeling EVERYTHING and doing it right with 5200/4000 ( 4000 is the quick set version of 5200 and is JUST as awesome) and stainless 1/4-20 hardware to mount the pump down to the boat then use fiberglass peanut butter to fill in any voids or gaps left after that. Will be a lot stronger, cleaner and will give me a better piece of mind. Will also allow me to replace my rotten transom wood with a piece of .125 aluminum to completely delete any and all wood from the boat for good.


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## Flat_Bottum (Mar 2, 2015)

Got most of the engine pulled away from the ski hull and ready to be removed in the morning. While taking the impeller out of the pump, I noticed that I have a crack in one of the blades. I will try to repair it but if I can not, it will be time for a new one. The rest of the impeller looks great so I am hoping that I can repair it and be good to go. While thinking and planning out the transom repair tomorrow, I have come across a possible issue. There is still one remaining transom supports which I did not remove when building it originally. Now, I will never have an outboard on this boat again so will it be ok to remove this last support? Its one from the floor to the transom. I will be bracing the transom on the sides once I install the aluminum back there but not sure if that will be enough. There is no thrust pushing on the transom anymore so not sure.


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## DarynCashmark (Mar 2, 2015)

That is a super cool project. I wish I was more mechanically inclined. I would love to have a jet boat to fish shallows. Good luck on the build. It looks like it will be awesome when it is done.


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## typed by ben (Mar 3, 2015)

I used tuff coat on my tin project. It works just like painting any other bare metal- scuff, etch primer, then paint away. it's pricey compared to traditional paint but the finish adds a lot of value and utility to what would otherwise look like a homemade boat.


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## Flat_Bottum (Mar 5, 2015)

Thank you for the information. I just want to make sure that however I finish the interior will be able to withstand some good abuse without chipping, scraping or peeling away. I busted my rear these past two days to get some more work done. I was able to remove the ski hull from the boat, clean everything up, resize the boat hull cut out as well as redo my transom so as to delete the drop down that it used to have for the outboard. Here are some photos. Should be dropping motor back in tomorrow morning.

Here is what it looked like under the ski hull and boat hull. I will never again use expandable foam on a boat it I can help it.







Cleaned everything up and resized the boat cut out. Even reformed the boats hull to better fit the ski hull. This drops the pump down about 1.5-2" lower into the water.


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## Flat_Bottum (Mar 5, 2015)

There is now no more wood on the boat at all. The transom plate I cut out is .188 aluminum which is riveted to the boats existing transom with a nice layer of 5200 in the middle. I couldn't get the hull to fit just right in the boat so I took a thin piece of rubber mat, layed down in the boat and put two quarts of short strand fiberglass filler on top of the mat. I then put the ski hull down into place and weighed it down to adhear the fiberglass to the ski hulls belly. I then used 5 (yes 5) tubes of 5200 to layer the boats hull where the ski would be touching and set into place. I used 8 1/4-20 stainless cariadge bolts to hold the ski hull down under the engine pan and 18 8-32 bolts to attatch the rest of the boats hull to the ski. All are 304 stainless with 304 stainless poly nuts on the top to pull it all together. Needless to say, once I tightened the ski hull down, I had 5200 running EVERYWHERE! Probably wasted a solid tube and a half BUT I know it is fully sealed and will not have a drop of water coming in from the bottom. I do have an hours worth of work with a razor once it cures to clean it up.


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## Flat_Bottum (Mar 5, 2015)

Got a little more work done on the boat this morning. Was able to drop the engine back in, install the pump and get my trim gizmo re-installed. I did not keep the factory trim hole on the ski hull so I had to fabricate a way to mount the motor inside the engine compartment of the boat and run a stainless rod out of the back of the boat to the nozzle. This is 3/8 NPT stainless pipe which the motor feeds the rod through. I am not using the factory suction bilge so I ran the original bilge lines to two pipe nipples I tig welded into place. This allows any water that comes through the trip pipe to be sucked right back out without getting into the boat. Its not pretty but it works good.


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## Flat_Bottum (Mar 7, 2015)

Started running the rear deck framing yesterday morning and hoping to get a good amount done over the weekend. I am having two problems that I am having trouble figuring out. The first is I am trying to decide whether to fully enclose the back of the boat or to just build a dog house for the engine and leave the sides open. Second is do I want to keep my center steering or offset like regular boats.


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## Flat_Bottum (Mar 9, 2015)

So decided to to the dog house style over the engine and leave the sides of the boat open in the rear. Also got the trim motor hooked up and should be full installed by tomorrow morning.


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## Flat_Bottum (Mar 14, 2015)

Got most of the rear dog house framed in and ready to go. Decided also to stick with center steering since I will be running the boat by myself a lot of the time and that not only keeps all of the weight centered in the boat but puts me up another 4-5" while driving so I can see better. Have to finish framing the floor supports then I will be ready to start cutting out the sheet, painting and installing. Getting closer.


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## tomme boy (Mar 15, 2015)

You might want to run a few more braces across the transom. Hate to have to go back and add them later.


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## fishin_magician (Mar 15, 2015)

Man you ate definitely getting it done... Its looking good thus far ...keep up the good work


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## Flat_Bottum (Mar 15, 2015)

Thanks, I have been doin my best to get this thing finished. I hear the river callin me haha. As for the transom supports, its fairly solid as it is. The engine compartment framing is attached to the transom in the center, jet ski hull is bolted to the transom which is bolted to the bottom of the boat and I have the two top corner supports which hold the top. If I was running an outboard on it I would be adding more support for sure but without any thrust or pressure being put on the transom, I should be alright.


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## Flat_Bottum (Mar 18, 2015)

Ordered and installed new diaphragm fuel pump for the boat, its the mikuni triple outlet. Keeping the electric in the boat just in case. Started running bow and transom lights and sending unit wiring. Should be starting the floor and decking in the next few days and will update everything with photos here soon. Shouldn't be too much longer.


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## ColtonS (Mar 26, 2015)

Your straight piped exhaust has gotten my attention..... I too have a polaris 750 in my boat and would like to know if there is any advantage to removing the muffler :-k


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## Earlo (Mar 26, 2015)

Flat_Bottum said:


> Also, I will not be using any carpet in this boat and would like to know what sort of paint are you guys using for your carpetless decks and floors that provides good life from peeling or scrapes? I dont want a paint that is going to come up just by sliding a tackle box across it or something.



Nice looking build. I have a Weldbilt I added a floor and front deck to, and used some concrete deck paint from Lowes called Restore 10x. Nice and skid-proof, does not get too hot, stands up to the carwash and feels great on bare feet.


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## Flat_Bottum (Mar 28, 2015)

Awesome, thank you fro the paint recommendation. As for the exhaust for my engine, I have no idea if there is any pros or cons to making it straight piped. I wanted to use the factory muffler but I was not able to considering the exhaust exit comes out of the top. Engine seems to like it but it is loud...like really loud. If you click on one of the videos in the very first post, you can see and hear the boat run and see what she sounds like. The exhaust exit is a couple inches in the water what sitting but is fully out of water on plain.


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## ColtonS (Apr 1, 2015)

Wow....I am surprised at how much different yours sounds than mine. I'm probably gunna make me a straight pipe now to leave in the boat for when I want to swap out and play a little.


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## JL8Jeff (Apr 1, 2015)

I had an old Boston Whaler Rage 13' jet boat with the Yamaha 650 jetski engine in it. I added a Pro-tek wake up kit which included an exhaust manifold, higher compression head, carb modifications and ran a 2-1/2" straight pipe. It sounded a like a pro-stock jetski and got old quick. I bought a 2-1/2" water injected silencer off Ebay cheap and routed cooling water to it. I put a valve on it so I could adjust the amount of water and got the perferct combination of sound and power. It looks like you could add a silencer to your pipe if you wanted to.


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## Flat_Bottum (Apr 1, 2015)

The only reason I straight piped mine was because I could not use the factory muffler. If I could have then I would have. I will look into that one you say you found on ebay. It is loud and does get annoying really fast. The pitch is what gets me after awhile on the throttle, a deeper tone would be nice. Thanks again.

As for boat progress, it has been a bit crazy lately with life in general and getting my Four Winns up and running for a striper trip. Should be finishing floor supports in the next few days and then will be looking to start welding up all of the framing. I dont trust just the pop rivets because eventually they will rattle loose and I dont want to deal with that.


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## CedarRiverScooter (Apr 2, 2015)

FB - Somehow I was missing this thread up until today. 

Your boat is looking great! I bet you don't have the same cavitation issue I am getting due to your V hull. I will be putting in same reverse gate you have. What are you going to use for a steering control - teleflex?

Kep the pix coming!


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## Flat_Bottum (Apr 2, 2015)

I had really bad cavitation on the first shake down run...like anything over a ripple and I would struggle to keep the boat in the mid to low 30's MPH. I added a small scoop to the very back of the factory grate and that help hook up out a lot but I lost a few MPH on the top. Since the rebuild of the boat, you can see that I use a hammer to bow and bend the hull of the boat down into the water a little bit which sort of created a type of spoon, but not really a spoon if that makes sence. I am hoping that it helps out so I can run the factory grate again but we shall see. How bad is your cavitation right now? For my steering, I am using the factory steering cable and factory console which unbolts from the ski hull. I made a small adapter and mounted a 10" aluminum buttefly steering wheel. Worked out really really good and I love it. Doesn't look the best but I have less than 1/2 turn full lock to full lock which makes navigation a breeze.


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## Flat_Bottum (Apr 2, 2015)

Also, my hull isn't a V...but its not a true flat bottom. I have not been able to identify the actual model of the boat since I have owned it. The front of the boat is not a V but its not a jon style neither but it does have a decent V coming down the bow but it flattens out almost immediately. The boat is a 1444....so I don't know what it is haha. Works for me though.


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## Flat_Bottum (Apr 3, 2015)

So hopfully in the next couple of days I can finish my floor supports. Problem is, I am not trusting the pop rivets to hold tight for very long. So, I was thinking about welding all the joints for added support but would have to ARC them since I dont have access to an aluminum MIG. So, has anyone done this with success? I used to do it back in the day but it was thicker material, around 1/4". Or will the rivets be just fine?


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## CedarRiverScooter (Apr 3, 2015)

I have an old millermatic mig machine that I jury rigged to run aluminum. Got it done, but if I stayed in one spot an extra second there would be a hole. I would think that stick would be just as hard to control on thin material. Could you rivet it together & then take it to a weld shop & them add some inches? Belts & suspenders!


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## Flat_Bottum (Apr 3, 2015)

Thats what I was thinking about doing...but I have issues with trusting other people to work on my things haha. I have done it before but like said, it was thinker material. Whenever I needed to weld aluminum, I just always used the TIG at work. I have a welding shop by my house and will prob rent a small arc welder for a day or so to give her a shot, if it doesn't work out then I will see if they do aluminum. Id just hate to have the deck start rattling after one trip...that would suck.


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## Flat_Bottum (Apr 7, 2015)

New bildge pumps came in, will be running a 750 GPH pump on either side of the transom. Also found a buddy at work who had a lincoln mig that I can borrow and set up for aluminum. This will make everything so much easier and stronger in the long run. Should have some photos up soon.


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## CedarRiverScooter (Apr 8, 2015)

I got my mig to do aluminum by getting a teflon liner (they don't give those away) & also using an oversized tip (i.e. .045 for .035 wire). I also had to use 5356 wire because the 4043 was too soft to feed. 5356 wants to crack, so beware. I turned my 150 amp machine wide open & only got spray transfer, but it did work. Any less power = no penetration.

Good luck!


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## Flat_Bottum (Apr 8, 2015)

Im still debating. I know that I need to do something other than just the rivets. I do have a couple packages of SS 8-32 bolts that I was just going to use to bolt everything together with countersunk heads but still not sure. I have a couple days before I can get back on it so the next few days will tell.


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## Flat_Bottum (Apr 11, 2015)

So I have decided to weld it, one way or another. I rebuilt the boat to do it right since I didn't the first time and I dont want to start cutting corners now just to fight it later. Also, my bilge pumps came in. Will be running dual 750 gph pumps, one on either side of the ski hull in the back of the boat. Once I get them wired up, I will be putting both water hoses on full into the boat and kick them on to see how they do. I want over kill for the boat.


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## Flat_Bottum (Aug 12, 2017)

Well I tell you all what...this has been a pain in my rear and one of the looooongest unfinished projects of all time! I changed positions at work and was brought into management. That alone took each and every minute of my spare time away. After a while of that, I came back to a basic tech to get away from the office and back on the floor. Then I moved, had a baby boy and now FINALLY pulled the boat back out of the garage to finish. It has not changed since the last post but I am hoping that changes ASAP! Glad to be back sharing and reading all of the other awesome projects posted! My immediate plans are to power wash all the dust and cob webs out of the boat, build up a console and then drag it down to a local fab shop where they will be welding her all up. Pictures to come soon I promise.


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## CedarRiverScooter (Aug 12, 2017)

I hear ya - I have way more time in building my JJ than I will ever spend using it!

That said, it is my favorite toy.

So keep the project candle lit.

Being in middle management can be challenging, you get pulled from both sides. Glad you are back in a position you are comfortable with.

How's the kid? Just wait until you teach him how to run the boat, better yet when he pulls you skiing!


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## DirtyD (Aug 13, 2017)

I appreciate your comment on my thread. If you find some time, I would love to see what you did with the loader grate. Not so much as to pinch your idea, but to save me some potential head scratching.


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## CedarRiverScooter (Aug 13, 2017)

My 1st try had the intake grate pretty much flush with flat bottom - you can easily guess how much that cavitated. The next winter I cut it back apart & lowered the intake are about 1.5 inches. I fabricated a tapered panel, kind of like a vee, to make the transition. It worked great. Another change I made was to remount pump angle to fix porposing.

If I recall correctly, you have a mod V hull, so that should push air to the side well. Theat polaris 750 should push it to mid 30 mph.

Edit: I tried the 'top loader 'grate, if that is what you are referring to. It helped with cavitation but allowed big rocks in, bad for the impeller. I still have but have no use for it - it's yours for the shipping if you want it.


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## Flat_Bottum (Aug 15, 2017)

All I did was get a piece of 1/4" aluminum, grind one edge to a knife edge and then cut slots in it so when I slide it up inside my grate it would fit. I then tig welded it in place and called it a day. I will try and find pictures or it to show you. This time around though, I beat the boat bottom out to match the shape of the ski hull. This also dropped my unit down about 2" overall so that should help where I wont need to loader grate I made.

Family is doing good, just bout 12 acres of properly that has been neglected so I ALWAYS have a project haha.
Yes, I am a modified V which helps me out compared to a try flat bottom. I still needed to mold the bottom a bit to fit right. With a full 2x4 wood deck frame and 3/4" plywood for decking I pushed 44 mph on glass and about 33-35 on couple inch chop. With the grate I made I topped out at 41-42 mph on glass but maintained my high 37-38 in the same chop. I like this Polaris, not super high HP but idle to mid range this thing is a torque monster.


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