Pontoon Boat & Deck Boat Forum

So i was having a real bad issue with ventilation when I was at WOT. Originally if i was at WOT there would be a good chance the prop would lose grip and the rpm's would go up big time. Backing off the throttle would make things better again. This would happen if it was just me and the wife out or having a couple friends...would do it most of the time. I could not trim the motor at all (it was all the way down) without it ventilating. I could not see the top of the cavitation plate at WOT either, just the top plate of the lower unit. I would also get a ton of spray coming back over the sun deck, just water being thrown everywhere. The motor was mounted at the top holes on the bracket so it was in the water good.

I raised the motor up two holes (there is a total of 5 mounting holes) the other day and took her out this morning, just me and my friend. No spray over the sun deck but there was some water being thrown around. I could trim the motor more before losing grip. I still can't see the top of the cavitation plate at WOT but overall it was a big improvement from before. So I got back home and raised the motor up two more holes (it's now all the way up) and will take her out tomorrow. I'm hoping i have got the ventilation issue solved...

I bought a used engine hoist and that has been the best investment so far...otherwise I have no idea how I would lift the motor up without breaking my back.

Here are some pics of where the motor was mounted compared to the transom...starting with the lowest and working up to the highest.

Cavitation plate stiil way too low. Should be even or slightly lower than the motor pod on toon. I have a 90 Merc on a 20 ft Lowe and can trim mine up like a bass boat before it breaks loose. Top speed 27 GPS. @ 5800 rpm. Running 13x 16 pitch prop.

I could go up another 2 holes and that's with me drilling out the transom and making new holes....and seeing if the steering cable can be at an angle. maybe i need to look for a short shaft motor....

So taking the boat out today, at WOT the cavitation plate is just visable, pretty much what it should be. I have a couple more people and more gear than normal so I'm about 5mph below what I normally do.
So I think I have the height dialed in...small victories!

cool! What speed and rpm's are you seeing--and can you trim motor out any better?

So I took the boat out this morning without all that extra weight. It was pretty choppy and the wind was blowing, not the most ideal conditions, however I was able to get to 5500 rpm and a top speed of 18mph.
At WOT you can see the cavitation plate.
The only thing that is still a mystery is I still can't trim the motor much at WOT. I'm ok with it as long as the motor is in the right rpm range.

The one thing I need to fix is the opening on the starboard side on the transom where the steering cable and battery wires come through. It's a decent size opening and there is a good amount of water splashing through the opening.

I wouldn't worry too much about trimming. Remember, the primary purpose of adjusting the trim is to change the position of the hull in the water, not about changing the position of the motor. On a pontoon boat like yours, the two toons are displacement hulls that you're just shoving through the water, so you're not going to have that much effect on them by trimming.

steve1313 wrote: ↑

Mon Jul 20, 2020 2:47 am

I wouldn't worry too much about trimming. Remember, the primary purpose of adjusting the trim is to change the position of the hull in the water, not about changing the position of the motor. On a pontoon boat like yours, the two toons are displacement hulls that you're just shoving through the water, so you're not going to have that much effect on them by trimming.

I get a significant increase in engine rpm's and speed by triming my motor--definitely gets the nose of my boat up---less boat in water---more speed.

wwind3 wrote: ↑

Tue Jul 21, 2020 3:17 am

I get a significant increase in engine rpm's and speed by triming my motor--definitely gets the nose of my boat up---less boat in water---more speed.

Your boat is 16 years newer and has 50% more power than the OP's boat. That alone makes a big difference in the results you'll get compared to his boat. As far as RPM increase, you'll always get that with any motor as you trim up because you are moving the prop out of the water into the air, which provides less resistance, causing an RPM increase (and an eventual blowout).

steve1313 wrote: ↑

Tue Jul 21, 2020 6:23 am

wwind3 wrote: ↑

Tue Jul 21, 2020 3:17 am

I get a significant increase in engine rpm's and speed by triming my motor--definitely gets the nose of my boat up---less boat in water---more speed.

Your boat is 16 years newer and has 50% more power than the OP's boat. That alone makes a big difference in the results you'll get compared to his boat. As far as RPM increase, you'll always get that with any motor as you trim up because you are moving the prop out of the water into the air, which provides less resistance, causing an RPM increase (and an eventual blowout).

yep--power does make a big difference on pontoons. But I definitely get bow lift when I trim up and probably 5 mph faster trimmed out than tucked.. And at least 600 rpm's You are right tho'--cant overtrim or it will slow down--and you will eventually blow out,,