got too much motor

[Groo]

My 22' pontoon is rated for 75hp. I got it with a 28spl that wasn't running right. I picked up a new Suzuki df50av (like the bigfoot/CT/etc.)
The back end is way deep now, as in the logs are mostly submerged in the rear when running.
I see two solutions that don't involve selling my brand new motor or getting a completely new boat;
1) relocate the rather rearward captains station further forward, to put my heavy rear further forward.
2) get a 3rd toon or motor pod with some flotation instead of the flimsy adjustable height transom that is there now.

I am thinking option 2 would result in a better boat with less work, but probably a bit more cash.

I also found I am getting ridiculously low RPMs (3600 WOT) with the 13" pitch prop that came with the motor. As it is now I would be tempted to go with a 9" pitch, but I'm thinking may only need an 11" pitch if I get it sitting more level.

 

[GA_Boater]

What is the weight of the two motors? It can't be but maybe less than 150#. I'll answer my own question - about 125 pounds.

A passenger moving from the front to back when the SPL was on it would sink the back, too.

Was the toon low in water with the SPL?

Any water in the logs?

 

[Sea Rider]

Are there side water splashes or even over transom water splashes when toon rides with both back logs submerged, if so, that accounts for more water drag on lower tail which traduces in very poor rpm...

Happy Boating

 

[Faztbullet]

Add the 3rd tube...

 

[Groo]

I doubt there is water in the logs. that had never been a problem before (sitting at a dock all summer) and it was out of the water for months before being put in the water with the new outboard. It was also consistent from the beginning to the end of the ride. The crud line is less than halfway up the logs in the back, but deeper in the back than the front.

weight difference between the two motors looks to be 131 lbs, looking at the specks (251 from 121). it seems like more than the weight is in play.....the weight further back. Is that the issue maybe? looks like newer longer motor front is further back than the SPL too (so not just the added length). So the CG of the motor must be maybe 6" further back??

changing the trim didn't seem to have much impact.

now that it is back on land, I cut out a section of the shelf to get the motor higher, and was able to lift the transom another notch (2"?) beyond what I was able to do in the water. I like where the bottom of the rudder is now relative to the bottom of the logs, just below, and I can trim up if it gets shallow.
I could lift it one more notch, and it is also mounted on the lowest mounting hole, so I could raise it a couple of inches that way as well, but like I said, I like the way it looks where it is at relative to the logs. I just want more flotation in the back.

I wonder if moving the fuel and battery forward (under the front seats maybe) would be enough? I wonder how much fuel hose would be too much for the motor pump?

Looking at it again, adding much of a float would require a new trailer, so I'd rather not go down that road. I don't trailer it often since I normally just dock it at the house, so maybe something removable?

 

[ahicks]

So adjustable height transom means this is an older boat, and older boats most often use smaller tubes than what we now see being used most often.

Even though the boat is rated for 75 hp, I'd be pretty shy of an adjustable transom. Most are all steel that I've seen - and at 25 years old or so, I would give that a very careful going over. As well as what it's bolted to, and what is used to fasten it.....

 

[Groo]

I roughly measured the tubes to fall somewhere between 20" and 24". The boat also has cones on the back of the tubes (starting about where most tubes normally end) that should give some added flotation to the back. They are basically sponsons.

I saw no signs of the steel cracking on the adjustable transom, but I've thinking about getting some section of angle iron to reinforce it. The other thought is once I find the height where I like the transom at would be to make a heavier duty fixed transom.
Honestly, I think if a flaw turns up in the transom it will be from bouncing down the road on the trailer, instead of forces encountered on the water.

 

[MRS]

Can add a photo of what you are dealing with?

 

[ahicks]

Suit yourself on the mount. Myself, I think they were designed for engine weights and torque applications 25- 40 hp engines might have. Just keep an eye on it.

Re: tube diameter, there's quite a bit of difference between a 20" tube and a 24" tube when it comes to flotation. I have a 90 hp Honda on our 24' 24" tubes, and it does a nice job.

 

[Cat nip]

You could move the battery up front but i would not move the fuel up under a Seat due to safty reasons. There are options such as the water glide to help with buoyancy.

 

[Scott Danforth]

jettison the adjustable transom and get a verical jack plate like one from Bobs Machine shop. this will bring the motor a bit forward as well as give you vertical adjustment

move the batteries forward

raise the motor to the optimum location prior to playing with props.

I personally would have looked for a 2-stroke

 

[Groo]

Suit yourself on the mount. Myself, I think they were designed for engine weights and torque applications 25- 40 hp engines might have. Just keep an eye on it.

Re: tube diameter, there's quite a bit of difference between a 20" tube and a 24" tube when it comes to flotation. I have a 90 hp Honda on our 24' 24" tubes, and it does a nice job.

a 75hp 2 stroke from when this was built is better than 50lbs heavier than the df50av, and I've got to think capable of quite a bit more thrust.

 

[Groo]

You could move the battery up front but i would not move the fuel up under a Seat due to safty reasons. There are options such as the water glide to help with buoyancy.

If electrical is not near the tanks, I don't see a risk, especially if I vent it a bit more. I was more worried about the fuel pump might not be able to draw the gasoline that far. Where the tanks go now is right by seating as well.

I've considered something like a waterglide. Any idea on the price of those?
1 downside of one of those it that I'd have to modify my trailer somewhat significantly.

 

[Groo]

jettison the adjustable transom and get a verical jack plate like one from Bobs Machine shop. this will bring the motor a bit forward as well as give you vertical adjustment

move the batteries forward

raise the motor to the optimum location prior to playing with props.

I personally would have looked for a 2-stroke

I believe the main reason for the adjustable transom is the old engine didn't have remote pitch control. I am hopeful I'll be able to just pitch the motor up when I get into shallows. Basically, If I redo it all, I am hopeful I won't need a jack-plate.

no viable new 2-stroke option near me. I was looking at Suzuki or Yamaha. I probably would have gone 4 stroke anyways. I love the quietness of this engine.

 

[Groo]

Raising the motor got it riding level, but did nothing for the RPMs. I wonder if the tach isn't reading right or maybe the engine isn't going WOT.

looking at the ratios I wouldn't expect just changing from a 13 pitch to a 9 pitch would be enough.
It also felt quite a bit faster than the old 30hp and was making significantly more wake. I would figure a 50 hp running just over half RPMs would be making about 30hp, so the speed should be comparable

 

[Groo]

I'm thinking the tach might be set up wrong, as in expecting 2 pulses per rev and getting 3 from my engine.
If that the case, my WOT is right at the bottom of the range. The dealer will be looking into that possibility for me, but I called him Friday afternoon to discus it, so not too surprised I haven't heard back yet.

 

[Groo]

no. it wouldn't be 3 when expecting 2. that would be reading high, but maybe something similar