# what should a new 15hp 4 stroke do on a 1436 jon ?



## back4more (Feb 27, 2014)

just upgraded our 2013 6hp 4 stroke tohatsu to a 2014 tohatsu 15hp 4 stroke for our alumnacraft 1436. we took it out for the first time last weekend. after hitting the 2 hour mark on the motor I opened it up to WOT for maybe 35-40 seconds. using my lowrance mark 4 gps I found that the speed topped out a little over 17 mph. for a split second I thought it read 20 mph, but it was quick and I didnt see a 18 or 19 at all, but when it was reading 17 the reading was 17 constantly.

so we went from 13mph with 6hp to 17mph with 15hp (+ 135 pounds total weight too)

shouldnt I more of an increase with the 15hp 4 stroke?



1436 w/ 2013 tohatsu *6hp* 4 stroke - *13+ mph* (phone gps)
minimal chop, 545lbs in boat


Spoiler



- 480lbs 3 people (2 on mid bench, 1 on rear bench), 60lb motor, ~5lbs 3 life vests



1436 w/ 2014 tohatsu *15hp* 4 stroke - *17+ mph* (lowrance FF/gps)
very little chop, 680lbs in boat -


Spoiler



- 480lbs 3 people (2 on mid bench, 1 on rear bench), 115lb motor, 50lbs 3/4 sheet 3/4in plywood w/ carpet, 10lbs medium cooler w/ sm emergency paddle, PWC fire extinguisher, small battery for FF, 20lbs fuel tank/fuel, ~5lbs 3 life vests


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## Boat2fast (Feb 27, 2014)

Seems slow...but, that's a lot of weight. Need to check the set-up on the prop. Find your operating range and check your RPM. If you are running too much RPM, you need more pitch; too little RPM needs less pitch.


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## TNtroller (Feb 28, 2014)

Try making a test run with the 15 and the same weight as the test run with the 6hp for a better comparsion. Sounds like you need to move some weight up to the bow, maybe one of the smaller passengers if possible, or a cooler with some ice/water, or milk jugs with water, etc, to try some weight distribution and see if that helps.


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## DrNip (Feb 28, 2014)

Looks like you asking a whole lot out of that 1436 and 15 HP with 3 people and all the excess weight. Was the 3 people just a test for the engine or are you actually out fishing with 3?


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## bcbouy (Feb 28, 2014)

my 14' v hull does near 20 mph. with a 2011 15 2 stroke wot with nearly the same weight.id say its right where it should be.imho messing with the prop is wasting time and money .throttle back and enjoy the ride :LOL2:


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## scoobeb (Mar 1, 2014)

That boat should fly even with that weight in it.I have a 1436 with a 20hp and it does near 30mph with me and near 28mph with 2 but with 3 it would probably be near 23-25mph.The 15merc/tohatsu(same motor) has a ton of power and you should do near 20-23mph with no problem.


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## bcbouy (Mar 1, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=343273#p343273 said:


> scoobeb » Today, 13:37[/url]"]That boat should fly even with that weight in it.I have a 1436 with a 20hp and it does near 30mph with me and near 28mph with 2 but with 3 it would probably be near 23-25mph.The 15merc/tohatsu(same motor) has a ton of power and you should do near 20-23mph with no problem.


i respectfully gotta call bs on that. theres no way a 15 horse can get those speeds with #550 weight.especially a john.my 9.9 didn't get those speeds pushing a 120 pound 12 footer.


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## scoobeb (Mar 1, 2014)

I have had a 15hp 2stroke merc on a 1436 that did near 28mph,you need to watch youtube my friend you will learn alot.I have seen a 15hp 4stroke nissan(same as the tohatsu and merc) with 2guys in a 1436 and they were flying.A 1436 is only 150 to 200lbs.If you can't get over 20mph with only 500lbs of weight in the boat then there is something wrong with that motor or it's propped wrong.Trust me on that,you can call b.s all you want but the facts don't lie.If you watch you tube there is hundreds if not thousands of videos with a 15hp moving well over 500lbs of weight well over 20mph.

A 15/20hp is a lot more powerful then people give them credit for.Like i said if anyone is having an issue getting over 20mph with only 500lbs of weight there is an issue with that motor.I weigh over 300lbs plus the motor i have is 106lbs and i had a 200lb other person on my boat,a 1436 crestliner which weighs all of 185lbs and top end was near 28mph with a 11pitch prop and it had an awesome out of the hole shot to.That is near 800lbs including the boat weight,just in the boat was near 600lbs and i hit near 28mph so numbers don't lie.I forgot to add it was a dead calm flat day,not a drop of wind so that can come into play,as with the tide to can also alter speed,if your going against the tide and the wind that can take some speed off what you could normally do.To get a true speed go on a flat calm day.A 15 would probably be a few hairs slower at say 24-26mph.They are the same outboard except for the carb.


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## bcbouy (Mar 2, 2014)

so there you have it,back4more. our motors are broken and the numbers are wrong.


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## scoobeb (Mar 2, 2014)

Go to youtube and you will learn alot my friend,the numbers don't lie.There is a guy with a 1236 and he has a 1976 9.9 2stroke johnson and he put a 15hp carb in it,with one person again he went close to 26mph and with 3 people and a dog he hit 21.1mph.He had the max of almost 550lbs in it.Look all over youtube there is hundreds if not thousands of videos that show the speed of a 15hp.

I had a 9.8hp 2stroke tohatsu on a 1236 which is like 20lbs lighter then a 1436,with two full adults,me at 250lbs at the time and my brother at 240lbs which is near 500lbs plus all the gear on the boat,tackle,bait bucket full of water,2 coolers,trolling motor,etc... we were at exactly 20mph so you can't tell me that it's not right.

I'm not going to debate this with you but 500lbs is not alot of weight in a boat and if a 15hp can't go past 17mph it's either propped wrong,there is way more then 500lbs in the boat,or the motor is not working right.There is no other reason,That is a 100%fact.


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## scoobeb (Mar 3, 2014)

I found another one,15hp merc on a 14ft tracker,2 adults,2 children,battery,trolling motor,4 seats,all fishing gear,coolers,etc,they went almost 24mph gps,numbers don't lie again.

Hey Back4more if you want to learn alot go to youtube and find out what those guys are doing compared to what your doing,it may be as simple as a prop change,i go to youtube and ask questions all the time and many people have helped me out to get the most out of my engines.There is alot of smart people there as there are here,but you haven't really got enough info to fig out why it's only going 17mph because i'm telling you that is not right unless u have like 800-900lbs in the boat,or your way over or under propped.The bigger the prop the more speed you will get but the slower the whole shot along with as lower rpm,with a smaller prop the opposite happens,more get up and go and usually slower top end speed but your rpms will be higher.Remember your more then doubling your hp from a 6hp to a 15,a 4mph gain just doesn't sound right for the 9 more hp you gained.

You get to see live videos and they show the speeds in almost all the videos,plus you can see how the boats are loaded with gear and people.That is going to be your best bet.


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## DrNip (Mar 3, 2014)

We get it already, the numbers don't lie and go to youtube, lol.


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## scoobeb (Mar 3, 2014)

I'm just trying to help the guy,lol.


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## back4more (Mar 3, 2014)

Thanks for all the input everyone. I understand that weight has a lot to do with the speed, and prop does too. I was just surprised to find that my 6hp pushed us at 13 mph but the 15hp will only do 17 mph with just 135 lbs more. Not what I had in mind when I sprung for the costly upgrade. I can understand not getting 28-30 mph with the weight I had in the boat, but a 4 mph increase isn't much considering the motor difference.


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## turbotodd (Mar 3, 2014)

Friend of mine has a 20 hp Tohatsu (same motor but with 5 extra HP), power tilt even...on a 1448. With just me in it and nothing else (seats out, etc) with the stock prop, it runs 23 mph at 5700 RPM. 9" prop is what came on it.

I can't imagine a 15 on a 1436 being much slower unless the hull is severely hooked or damaged. Assuming the 15 came with the same 9" prop.

For the dude who had one running close to 30 mph, what prop is on it? Just curious.


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## scoobeb (Mar 4, 2014)

11 pitch prop on my new 20hp suzuki gave me near 30mph,it was like 29.7mph for like 20 to 25 seconds in the calm part of the water,it was dead flat calm out of the wind,when i went back into the wind it dropped to 27.6mph for a constant average speed.The suzuki is one of the most powerful engines for it's size that is out there,plus it helps it's only 97lbs.


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## scoobeb (Mar 4, 2014)

Remember the tohatsu can run near 6300 rpms,a 9pitch prop is way to small for that motor.I believe it's a 9.8pitch that comes on it,so it's near a 10pitch prop,go with a 11 and you should get over 25mph.There is a guy on youtube with a 1652 lowe jon boat at 450lbs and with 4 people on it he says it planes good with a new 20hp 4stroke merc.That to me is impressive.A 1448 jon boat is only like 260lbs unless it's all welded and a 20hp tohatsu should make that boat fly with one person.

There is a guy with an all welded monark 1448 with a 20hp 4stroke merc,same as the tohatsu and he's going 27mph across the water.So these speeds are very capable if you are propped right.


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## flatboat (Mar 4, 2014)

Check your motor height. Cavitation pate should be flush with bottom . With most boats you need a small block under the motor to get it right . There is a lot of drag if it is to low . I've had 7 boats everyone has had to be raised to get it right . Use a tac to check rpm's Buy prop that runs at the top of the top of that range , the guys that build them tell you where they run the best . Every boat is different it takes time and effort to get things right on your boats setup , weight distribution is very important In small boats if it's wrong it's a barge , if it's right it's a rocket , speed is the indicator of correct set up . If you increase from 16 to 23 mph with proper set up think how you have increased you mpg . That's why you bought the new motor to go faster with better economy ....
As always just my opinion


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## lovedr79 (Mar 4, 2014)

my heavy as aoll get out grizlly 1448 SC with floor and a merc. 20 will only go around 23 with two people loaded. I have my plate about 1" or more above the bottom. I also switched to a 4 blade which made planning a lot easier. with the stock 10p nothing in the boat at all I got 27 once in dead flat still water.


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## bcbouy (Mar 4, 2014)

fftopic: the op doesn't have a 20 hp.why do you keep comparing a 20 to a 15? 5 hp is 25% more power.put a 20 on an 18 ft. boat then compare.


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## back4more (Mar 4, 2014)

thanks again for the input everyone.

sorry for not answering this earlier ...


[url=https://www.tinboats.net/forum/viewtopic.php?p=343121#p343121 said:


> DrNip » 28 Feb 2014, 09:11[/url]"]Looks like you asking a whole lot out of that 1436 and 15 HP with 3 people and all the excess weight. Was the 3 people just a test for the engine or are you actually out fishing with 3?


my wife, daughter and I were just out cruising, something we plan to do a lot.

also, the 15hp does have a doel-fin stabalizer. Ive had a couple jon boats before with 9.8-9.9's and they were difficult when I would go out alone.


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## DrNip (Mar 4, 2014)

Well I would think that you could get at least 5-7 more mph of it with the 15 hp.


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## back4more (Mar 4, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=343728#p343728 said:


> DrNip » 11 minutes ago[/url]"]Well I would think that you could get at least 5-7 more mph of it with the 15 hp.



sorry if I wasnt clear, the 17mph was with the doel-fin installed on the 15hp.


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## scoobeb (Mar 5, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=343657#p343657 said:


> bcbouy » Yesterday, 09:52[/url]"]fftopic: the op doesn't have a 20 hp.why do you keep comparing a 20 to a 15? 5 hp is 25% more power.put a 20 on an 18 ft. boat then compare.


I was commenting on turbotodds post with his friend having a 20hp tohatsu.Plus he asked what prop pitch i was running,Did you miss that post?Also i only talk about a 15hp through out this whole thread besides what question i answered again from turbotodds post,that's it.

The only thing i said was that the 15/20hp merc or tohatsu was the same engine except for i believe the carb is jetted different.

Just for more info,tohatsu makes,of course tohatsu,nissan,and mercs up to 30hp,they also make all,yes all or evinrudes 4strokes up to 15hp,all they are is tohatsu's with evinrude stickers on it and they sell them for hundreds more like the mercs and nissans.That's why i get a kick out of people who say the merc is way better then a tohatsu or nissan when tohatsu makes their motors up to 30hp.A lot of people don't know these facts.

The difference in speed between a 15hp and 20hp is very minimal,a few mph at best.Even though it's a 25% increase in power,that's really what the 20 will give you over the 15,more torque when more weight is in the boat that the 15 will struggle with to get you on plane.You will be able to get on plane with the 20 way easier then the 15,but as far as overall wot it's a very minimal gain at best.


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## Rat (Mar 5, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=343289#p343289 said:


> bcbouy » 01 Mar 2014, 17:39[/url]"]
> 
> 
> [url=https://www.tinboats.net/forum/viewtopic.php?p=343273#p343273 said:
> ...



My 12 footer with a 9.9 4 stroke would run 26 mph all day long with me and gear. With an extra person and gear she would run 20 MPH. 
The RatKraft, 14 footer decked out, with a 20 HP will run 24 MPH and 20 MPH with an extra person. 

You could have several problems:
1) As stated above, incorrect pitch will have a huge effect; heavy boat go heavy on pitch.
2) Make sure you are hitting the RPMs for the motor, again this is pitch
3) Make sure the motor isn't too far below the chine, the ventilation plate should be even or just above the bottom of the boat for best performance. 
4) Do you have a Dol-fin (or similar) on the motor? If so, it should be out of the water when on plane. 

I don't know what you should be getting but you should see a better increase than 4-5 MPH from a 9.9 to a 15 HP; unless the 9.9 was some kinda wicked good motor.


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## back4more (Mar 5, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=343808#p343808 said:


> Rat » Today, 11:49[/url]"]
> 
> My 12 footer with a 9.9 4 stroke would run 26 mph all day long with me and gear. With an extra person and gear she would run 20 MPH.
> The RatKraft, 14 footer decked out, with a 20 HP will run 24 MPH and 20 MPH with an extra person.


You could have several problems:
1) As stated above, incorrect pitch will have a huge effect; heavy boat go heavy on pitch.
*sorry for such a noob question, but you mean whats referred to in the motor manual as the trim angle ?*
2) Make sure you are hitting the RPMs for the motor, again this is pitch
*will work on this after pitch is determined*
3) Make sure the motor isn't too far below the chine, the ventilation plate should be even or just above the bottom of the boat for best performance.
*my ventilation plate is really close to even with bottom of boat, checked it with a level last night* 
4) Do you have a Dol-fin (or similar) on the motor? If so, it should be out of the water when on plane. 
*I do have a doel-fin installed. I will check next time Im out to see if its out of the water on plane*



> I don't know what you should be getting but you should see a better increase than 4-5 MPH from a 9.9 to a 15 HP; unless the 9.9 was some kinda wicked good motor.


my 4 mph increase is going from a _*6hp*_ to 15hp


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## Rat (Mar 5, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=343864#p343864 said:


> back4more » Today, 17:57[/url]"]
> 
> 
> [url=https://www.tinboats.net/forum/viewtopic.php?p=343808#p343808 said:
> ...



1) & 2) Pitch refers to the pitch of the propeller not the tilt or trim of the motor. A boat only has one forward gear so imagine that the one gear was equivalent to 1st gear in a truck; this would be great for a truck that always pulled heavy loads but not good for one that wanted to go fast or pulled light loads. Now imagine if the truck only had third gear; you could get much more speed than the one with only 1st gear, but you could not pull a heavy load. This is what prop pitch is doing, changing the gear ratio. 
Read this article: https://www.comprop.com/pickprop.html

Getting the most out of your motor is all about getting the right pitch (gear) for the boat; and how we do that is by using the engine max RPM at WOT. You will need a tachometer like this, https://www.tinytach.com/. It doesn't need to be mounted or anything you can just hold it in your hand for the test; it is good to have a tachometer though so I recommend mounting it in the boat. 

A) Look at the prop you have now, there will two numbers stamped on it; the first is the diameter and the second is the pitch. As a rule you will keep the same diameter (within 1/2 inch anyway) but change the pitch to tune the drive. 
B) Hook up the tachometer
C) Load the boat with what it will normally be carrying
D) Run the boat at WOT and make note of the RPM and speed
If the test shows you are not making it to max RPM you need a lower pitch (down shifting) and visa versa. Each inch in prop pitch will make about 150-200 RPM difference. 

Some recommend removing the Dol-Fin for the tests but I haven't seen any interference when I have done this type of tune by leaving it on. Just make sure that it is out, or mostly out, of the water when on plane. 
If not you need to raise the motor to get it out of the water when on plane. I use 1/2" battens and paint stirring sticks to fine tune the height on the water. 
A) I raise the motor 1/4" at a time until the motor starts to ventilate in tight turns, then back it down 1/4"
B) Later you can build a permanent shim for the top of the transom or add a jack plate
C) There is a great tutorial for a DIY Jackplate here: Homemade Jackplate
You may end up with the ventilation plate higher than the bottom of your boat, that's okay. Tuning the height will ensure the motor is at the right depth so there is minimal drag but it is low enough that you don't ventilate and over-rev the motor in turns. This should be done before the prop tuning. All of mine end up above the bottom of the boat somewhere between 1 to 2-1/2 inches usually. 

Once you know the right prop pitch you can keep a lighter pitch in the boat as a back up and you can swap them out easily for when you are running light. I kept a light pitch on my motor because I usually ran light and my back up prop was heavier for those times I was going camping and had heavy loads. I am hard on props, so I always had a spare for those time I broke a blade or spun the hub. Keep a wrench, cotter pins and an extra castle nut in the boat as well; eventually you WILL drop one of these over board and it's nice to have a spare!


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## back4more (Mar 6, 2014)

thank you very much for the detailed information Rat. Im going to stay away from buying a new prop right now, but will revisit the idea in the future. Ive already bolted the motor to the transom but may go for the jack plate, if needed. that homemade plate looks nice.


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## scoobeb (Mar 7, 2014)

Be careful with using the dolphin,even know it's unlikely the cavitation plate can snap.Those dolphins do put as lot of pressure on the cavitation plates.Like i said it doesn't happen very much at all but it could.I have never used one and never will.I will do everything in my power to get the motor mounted right or change props before i do that,if that won't work i will sell the motor and buy a 2stroke.I have never had those issues of power loss though.Every boat i have ever had the motor sits around 1 inch below the bottom of the boat or dead even and has ran like a rapped ape.Weight distributed the wrong way is the only issue i have ever had.A dif prop can do wonders though in certain applications if needed.

Good luck.


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## back4more (Mar 8, 2014)

thanks skebob, I may try it without the doel-phin next weekend.

I took it out today and found out a few things.

first of the way I used a app on my phone (GPS Essentials) to determine that the 6hp pushed my empty boat and me 17mph. when I took out the 15hp motor, with wife daughter and I, I got my 17mph speed from my lowrance mark 4 ff/gps combo. today I found out that the two devices have a variance of as much as 2-3 mph.

when I went out alone I reached 20.0 based on the lowrance, and something like 22.9 using the phone app. I went back to the dock and changed my trim angle from the 3rd hole closest to the boat, to the 2nd hole closest to the boat. not good. I didnt even let the motor top out. the front was plowing water. went back to the dock and changed the trim angle to the 4th hole closest to the boat (as shown in pic below). this was much better, got me up to 23.3 mph. added the wife and daughter and we did 19.4 (compared to 17.3 or so last time)


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