porposing problem

[horizonlawn]

I've got a 18' thompson 18ss with a closed bow with a5.7 when i get it trimmed where i want it it porposes horribly. it gets to a point where the whole boat actually jumps out of the water and it gets scary. what can i do to fix this? id like to somehow fix my problem without trim tabs if possible. the fuel tank is in the closed bow, but it doesn't seem to matter if its full or empty. will a certain prop help? i'm running a aluminum 23 p now nothing fancy

 

[5150abf]

Re: porposing problem

Run your trim down and it should stop or get alot better anyhow.

If you trim the motor too much it tries to lift the bow but it is too heavy so it falls then tries to lift again on and on.

It is where the boat likes the trim that matters.

 

[tashasdaddy]

Re: porposing problem

Smart tabs will help also.

 

[Jdeagro]

Re: porposing problem

Horisonlawn:

Why don't you want to use trim tabs?

 

[woosterken]

Re: porposing problem

here is an article you mite want to look at.........

http://www.clubmarine.com.au/internet/clubmarine.nsf/docs/MG19-2+Technical

hope it helps

woosterken

 

[Nico2112]

Re: porposing problem

^^

Great article!

Thanks for sharing.

 

[gss036]

Re: porposing problem

Power Tech makes a 4 blade stern lifting prop. When I re powered w/ new 225Honda outboard, I had to go that route to get rid of proposing. Also had to raise the motor a couple of holes, you do not have that option w/a I/O.

 

[horizonlawn]

Re: porposing problem

I agree with trimming the boat to far up will cause problems, but when i trim it down enough to stop the problem the boat plows to much water. I guess the best solution is trim tabs, but i really didnt want to deal with the expense or time involed with trim tabs. I didnt think of the smart tabs. I don't know anyone who has tried these and i'm not sure i understand the concept of how the tabs know when to be down or straight. I understand that the force of the water would be greater when you are moving, but once your moving and there straight are they really doing anything, also do they create alot of drag affecting performance? are they adjustable? do they work great or are they a quick fix?

 

[tashasdaddy]

Re: porposing problem

just one of many threads on smart tabs, i have never heard anyone unhappy.

 

[Jdeagro]

Re: porposing problem

Horizonlawn;

How Smart Tabs work:

The size of the plate and the pressure of the actuator are coordinated with the size of the boat. Your boat would use either the ST1290-60 or the SX9510-60. From that point you can adjust the pressure (tune) to the needs of the boat.

At rest the tabs are held down by the nitrogen gas filled actuator, and provide immediate lift to the stern as the boat moves forward keeping the bow rise to a minimum.

When the boat reaches planing speeds the water pressure exceeds the actuator load and the plates are pushed up and run level with the bottom of the hull.

At cruising speeds the plates are still under pressure (although level) which provides enough ride control to eliminate porpoising and chine walking, they make the boat more responsive in turns, and ride smoother similar the suspension system on a car.

Since the pressure is adjustable (unlike a hydrofoil) excessive stern lift can be eliminated, or if more stern lift is required it can be increased.

The system is active 100% of the time and therefore works to keep the boat in the most efficient running position.

The top speed of the boat should increase about 5% if the motor trim is correct and the tab pressure is adjusted correctly. The reason for the increase in speed is due to two factors: 1, the boat will run smoother, and 2, the motor can be trimmed out more without porpoising. The prop angle will be more efficient.

Fuel economy will improve for the same reasons. In many cases additional top speed and economy can be realized with an increase in prop pitch since the trim tabs will improve the acceleration (hole shot ) significantly.

Installation can be done in an hour or less with minimal household tools.

If you would like more information feel free to call us at 800-233-0194.

 

[LubeDude]

Re: porposing problem

I agree with trimming the boat to far up will cause problems, but when i trim it down enough to stop the problem the boat plows to much water.

Does it "Plow too much water" enough to cause bow steering and thus lack of control or do you just not like the attitude of the boat with the nose down. If the boat isn't bow steering you may have no choice but to live without trimming up so far! Most I/O's that I have seen do not like too much trim!

 

[horizonlawn]

Re: porposing problem

I guess I don't really know what bow steering really means or feels like, but the overall feel of the boat seems like the bow is just to low, it feels like i need to lift the boat straight up when its trimmed properly(not porpesing). it is a older heavier boat that maybe my problem but it sounds like the smart tabs will help if not solve my problem.