Thompson plowing at full speed.

[Valv]

I have a 1991 Thompson Adventurer 288. We love the boat, the roominess, etc.
I have twin Mercruiser 260hp, which gives me 25mpg cruising speed and 30plus mph top speed
I only have a problem, when I push boat at full speed it starts to plow and, of course, it gets "squirly" and wanders all over.
I have trim tabs tucked all the way up, no drag in front that I can think of.
I can push almost 30mph then I have to back off and I am just at 4000rpm, and didn't let the boat get to full speed.
Plane occours at approx 24mph

 

[Capt'n Chris]

Re: Thompson plowing at full speed.

You have your "tabs tucked up?" If your tabs are down (tucked in), sure your bow will plow. Tell us where your tabs are as you describe.

 

[Valv]

Re: Thompson plowing at full speed.

As I said in my OP I had the tabs all the way up.
Thanks.

 

[cribber]

Re: Thompson plowing at full speed.

What pitch/type of props are you running? This could make all the difference in the world for handling since it looks like you have direct drive.

 

[Valv]

Re: Thompson plowing at full speed.

I don't know the pitch and I won't be able to know until I pull the boat from the slip, but how can pitch influence the positioning of a boat on water while at full speed ?

 

[Chris1956]

Re: Thompson plowing at full speed.

Do you have I/O motors that may be trimmed up, while under way? If so, they will lift the bow. On some boats it has no effect, however, my buddy had a 30' Thompson with twin 305 Mercruiser Sterndrives. He could get 40MPH, whne trimmed to optimim.

 

[Valv]

Re: Thompson plowing at full speed.

I don't have outdrives, I have twin 350s inboard with straight velvet drives.

 

[Ned L]

Re: Thompson plowing at full speed.

Hmm. interesting problem. Where are your tanks located & what are their levels? (Maybe fuel tanks aft & low, and water & holding tanks foreward & close to full?) Do you have much gear stowed below up foreward? Probably not, but you might check the chain locker to make sure you're not carrying a lot of water (weight) up there. - This has happened.
Has the boat always performed this way or is this something recent? I suppose you might check her bottom to see if it is hogged at all when you have her hauled for the winter. Are you sure the trim tabs are cycling all the way?