repowered toon from a 40 hp to 150 hp only gained 12 mph PLEASE HELP

[corysmith17]

I am in need of some help.I have a 24 ft harris kayot and just spent about 20 hours repowering it from a 40 hp yamaha to a 150 merc and i only gained 12 mph actual gps reading .My motor pod does not have the fins like i have seen on others could this be the problem if so ill make some and put them on .... but at what heights? also the 150 merc is a 1989 xr4 blackmax 20 " shaft, im only getting about 4100 rpms and im running a 17 pitch prop .I think im going to dump down to a 15 and raise the motor on the pod ... any ideas where the cavation plate should be in realtion to the bottom of the motor pod any help would be greatly appreciated .I am very disappointed ... I would like the boat to go at least 45 mph and 28 just isnt gonna cut it .Oh ya i only have 2 20" toons.PLEASE PLEASE HELP WITH IDEAS THANK YOU ALL FOR YOUR TIME

 

[Silvertip]

Re: repowered toon from a 40 hp to 150 hp only gained 12 mph PLEASE HELP

Well sir -- I hate to burst your bubble but getting 45 MPH out of that 'toon will take more than 150 HP (and a lot of courage). Triple toons with 150 and 175 Yamaha two strokes (Yamaha's test data) shows they are doing only 36-38 MPH. You only have two tubes. You might get 30 MPH with a proper prop but you cannot reasonably expect 45. You would be expecting to nearly triple the speed with less than four times the horsepower. That ain't going to happen.

 

[rickdb1boat]

Re: repowered toon from a 40 hp to 150 hp only gained 12 mph PLEASE HELP

I agree. You could expect 30 MPH or so with your setup. Reason being is that you only have 20" logs (more log in the water due to the small diameter = more drag) and there is only 2 of them. I'm guessing the engine is way too deep in the water. Have someone peek over the back when you are running at full throttle and see where the cavitation plate is in relation to the water. It should be right at the surface. The relationship of the plate to the transom will not apply in your situation. Also, I would move down in pitch prop to get the revs up to where they need to be, but only after you raise the engine to the appropriate height. Cause your RPM's will rise after you raise the engine. You will then be better equipped to tell how much pitch you should drop..

 

[5150abf]

Re: repowered toon from a 40 hp to 150 hp only gained 12 mph PLEASE HELP

As stated, not gonna happen, I have run a 25' tri with a 250 V-Max and it went somewhere around 42, a 25' with a Yamaha 350 went @ 54.

Pontoons aren't made to go fast as they aren't planing hulls, a mono hull lifts out of the water at speed, reducing drag, not so with a toon.

Speed on water is hard to come into so gaining 12 mph is pretty good.

Work on your prop and engine height, get your RPM where it should be and see where you are but don't get your hopes up for 45.

 

[MikDee]

Re: repowered toon from a 40 hp to 150 hp only gained 12 mph PLEASE HELP

Yes, A round bottom, as on the pontoons, is your worst planing surface. Flat is the Ideal surface, but it's also the bumpiest, that's why almost everything is a Vee bottom nowadays. If I had a Toon, Being the nut case I am for speed, I'd probably strap on a couple of 20'- 2"X8"s to the bottom of the toons, to get it planing better, or better yet, some wide aluminum angle iron, making a Vee, tacked, or welded, to the bottom of the toons.

 

[tashasdaddy]

Re: repowered toon from a 40 hp to 150 hp only gained 12 mph PLEASE HELP

MikDee i can see it now. making it a catamaran.

 

[Lone Duck]

Re: repowered toon from a 40 hp to 150 hp only gained 12 mph PLEASE HELP

MikDee i can see it now. making it a catamaran.

Yeah! And he would probably strap a cycle engine on each toon . And another for steering.

 

[redfury]

Re: repowered toon from a 40 hp to 150 hp only gained 12 mph PLEASE HELP

Hydrofoils on the toons, lift the whole thing outta the water and away you go!...might need a long drop jackplate though

 

[steelespike]

Re: repowered toon from a 40 hp to 150 hp only gained 12 mph PLEASE HELP

Gotta be dissapointed; but as suggested fine tune the height carefully adjust trim.Get everything right then a prop based on the results.You could add a belly skin or a 3rd toon.You do have the option to cruise at the speed of a 40 or 50 save some fuel and your motor will be loafing.

 

[rrhodes]

Re: repowered toon from a 40 hp to 150 hp only gained 12 mph PLEASE HELP

Are you sure your toon is even rated for a 150? 2 20" toons I would bet you are rated for 90hp or maybe 115hp. 24" Triple tubes are only rated for 150hp

 

[kenmyfam]

Re: repowered toon from a 40 hp to 150 hp only gained 12 mph PLEASE HELP

You are asking a lot from your toon wanting that kind of speed.
Correct set up is vital. Motor height, weight distribution etc. Select a replacement prop after doing the rest of the set up for best results.
Good Luck.