Repowering old 29' toon, going big HP, any handling thoughts ?

[calvinator]

Current rig, still a work in progress!
1989 Crest 29'. (2) 22" logs
Sundecker model, has the walk on upper deck.
Typically have 4 adults and 5-7 kids on there.
60HP motor. 10MPH on GPS when loaded.
In summary, this is a heavy toon and I travel heavily loaded with people.


My mission is to get to 18-20 MPH, the perfect speed for kneeboarding

I have $4000 budget.

Transom rated for 125HP.

I have my sights on a $850 good condition 1978 "Tower of Power" 135HP or a perfect $2000 1987 Yamaha VMAX 150.
I realize I'm a little over on the HP, I'm OK with that -- WOT runs are not what I'm after. I feel I need the HP grunt to get this 'toon to 20MPH in a short time. Just happens these two engines are top of my search list and within budget.

Need some thoughts here:

a) My only experience with this toon is SLOW. Any comments on handling this 'ol 29' toon with 22" logs going 20 mph? Is it no big deal -- is this dicey -- have to experience it on my own ????

b) No hairpin turns, just straightaways.

c) as always, any comments on my motor choices.

THANKS -

 

[dls322]

Re: Repowering old 29' toon, going big HP, any handling thoughts ?

Isn't 10mph fast enough?? LOL
I would double check the laws about running a motor that's more hp than your rating. You might get in trouble if stopped for a safety check. I'm sure they rate them specifically for a reason.
On my first pontoon, the transom was rated for a 90 and looking at the construction of it i would have been scared running a 40hp....after further inspection the transom actually had developed a large crack in it...and that was with the 75hp...and it was rated for higher!
Just a though because you don't want to loose your motor, which could really damage your boat and be a huge safety concern.

 

[TurboM700]

Re: Repowering old 29' toon, going big HP, any handling thoughts ?

I have a 24' with 23" tunes.

Here is my build.
http://forums.iboats.com/completed-boat-projects/pontoon-conversion-inboard-outboard-573089.html

She will do just under 30mph with me and 4 adults in it.

A few things I learned along the way.

You will want atleast a center tune in the front. Fast moving tunes with people up front can end scary when you left off the gas or get in some big wakes. Having the 3rd pontoon takes care of this issue.

You will want some kind of lift stakes to go 20mph. You will need to start to get this to plan.

Also plan on skinning the bottom of the boat so its smooth. This gave me almost 5mph on the top end since the water under the toon gets very turbulent.

I dont think 150hp will be enough to get you to 20mph I would think you will need at least 200hp. That's a big boat with alot of wind drag.

As far as the legal side of it goes. I have no clue as I stuffed a mercruiser 140hp in my boat when it rated for only 90hp.

I don't see how its any different they these guys with jet boats or power boats that build the motors for double the hp. Just don't do anything stupid and you shouldn't have a problem.

 

[Bamaman1]

Re: Repowering old 29' toon, going big HP, any handling thoughts ?

My old Starcraft 24' has a 115 hp Yamaha 2 stroke. It accelerates like a bass boat until it hits top speed where the Bear jumps on it's back. It'll easily pull skiers and tubers, but it handles like a pig in water.

I'd tell you to go with the newer Yamaha motor if it's in top notch condition. Be sure to have the lower unit pressure and vacuum tested to make sure you don't have to put $300 in parts and labor changing seals.

And make sure the new motor is the same length as the old motor. Nothing worse than putting too short of a motor on a pontoon boat only to get prop ventilation because it's the wrong length. You'll probably be looking at a 13 or 15 pitch prop.

 

[5150abf]

Re: Repowering old 29' toon, going big HP, any handling thoughts ?

Have someone knowledgeable examine the transom to make sure there are no cracked welds, one thing aluminum does really well is crack, it is super easy to fix but you have to find and fix them first.

You can imagine the forces a transom has to deal with, 115 horse full throttle from a dead stop, yikes.

Between the 2 engine the Yamaha wins hands down, newer, parts more available ect ect and they don't do anything scary, you have to go way faster than 20 get scared on a toon, never done it but I am told 60+ will get your full attention.