Pontoon Boat & Deck Boat Forum

I have a 2003 suncruiser trinidad, it's a 20' with a 2003 yamaha 90hp 2 stroke and I'm only getting 13-14 mph on GPS. I have searched and read and ended up with more questions than answers. I have had a bad tach and replaced it Saturday so I go great until 3500-3900 then from there up to 5500 it doesn't pick up speed. Seems like the prop is slipping or a ventilation problem. Here is the info I have. It is used in salt water, no under skin, 2 toons, the prop is a 13x13 3/4 or 13 3/4x13, it is all factory set-up, prop is new.


I am looking to see where to start like ventilation issue, then skinning bottom, then prop. I believe it should be able to go over 20-22mph oh I can grip over 3500 rpm.

Your boat should be running in the mid 20's. A 2 stoke 90 hp is actually the high end of horsepower a 20' boat uses, and the boat should also accelerate strongly. Your rpm's are about redline for a 2 stroke, and it's hard to believe the prop is hooking up.

You might want to have your prop inspected by a prop shop or where you bought it to see if it's slipping. Like you said, you may have a ventilation problem. I assume you have the engine trimmed down to where the anticavitation prop is at least parallel to the bottom of the toons?

You didn't say what kind of propeller you have. Your prop might be a bad match for a pontoon boat. Fortunately, a good aluminum prop is not very expensive.

After you get to the bottom of your problem, you might want to invest in aluminum sheeting for the bottom if you use the boat very much. They ride so much smoother and quieter underskinned.

Chris...just to give you something to compare it to, I'm running a yamaha 75 four stroke, also on a 20 footer, 2 people on board, smooth water and no wind... wot I get about 23 mph...

I have almost the same setup as you except mine is 22' long. Running the 13 5/8" x 13p Yamaha aluminum prop I run right at 22.5 mph per GPS.

Is your outboard mounted as low as it can go on the transom?

I am sure you really don't want to know this, but I am running a 9.9 with a 9 pitch and with just me and a light load I hit 12 mph on gps. In your case I would drop the motor lower to see if its captivating and not hooking up that would be my first thought.
From your description that would be my guess.

The prop is a 3 blade aluminum one, 13 3/4x13 or 13x13 3/4. I put the prop on about a month ago and has done this with the old and new prop. I will check the engine location. I plan on putting the sheeting underneath but I want to get it going right first. Anything else I should check for let me know. I can check Saturday. I appreciate the input.

Post pictures from the back showing the motor and transom maybe we can spot what is wrong before you spend any money.

margaritaman wrote:Post pictures from the back showing the motor and transom maybe we can spot what is wrong before you spend any money.

+1

im running right at 20 with my standard load. i could probably go up 1 pitch degree and get just that little bit more. but it wont be much. my boat is a 22' benny, 2 log.

Mine is a 90hp 2 stroke on a 24ft...have to agree that it almost sounds like the motor may not be in far enough and it's cavitating way too fast...with me and Jillie at WOT we get about 24mph....

It appears to be as low as it can go.

Yes that's how mine sets. Did you say it's a brand new prop? Is it tightened down well so the hub doesn't slip?

I was told to snug the prop only not to tighten it. Was that bad info, did I burn up the hub?

If you have spun the hub, you will notice it right away on acceleration. I think you are ok, here. Sounds like you are cavitating. Since you are all the way down on motor height, I would say thats a pitch problem. See what a higher pitch does for you. A little more cup, makes a lot of differerence.

And because of how your transom is made you have two choices, cut the center section out and replace with marine plywood so you can lower it, or buy a jack plate, and a jack plate would be my recommendation, A jack plate would be a lot easier to dial in.