Power Trim

[Derrick]

http://www.ryatraining.org/NR/rdonly...gpowertrim.pdf

I found this advice on the RYA site. May I request a debate/dialogue amongst all the experienced guys and gals on here? The advice is to trim the bow down in a head sea and up in a following sea. Up in a following sea seems to make sense to avoid "burying" in the back of the next wave. Down when approaching the steep face of an oncoming wave sounds a bit tricky. But maybe this works just fine if you know what you are doing. What does the team think and what do you do? I am not talking "perfect storm conditions" here just nice regular rows of waves 4-6ft within the capabilities of the boat and not ugly confused chop where all bets are usually off and a comfortable ride unlikely. Could be there are other issues being considered like prop ventilation and loss of grip on the water. ??????

[Pete7]

Worth having a read of this thread, we get to the right conclusion in the end. However in addition to trim you also need to use the throttle, at the right time and with care or you will go flying off a wave.

http://rib.net/forum/showthread.php?...ght=submarines

Pete

[Cookee]

Derrick - In my opinion the broad RYA advice is spot on, and as usual Pete 7 is as well concerning the throttle!

[Pablo]

I think a good way to learn the benefits of different trim positions is to drive a boat with a manual trim. You spend alot of time trying to find the best compromise for different situations.

[J S]

Originally Posted by Cookee

Derrick - In my opinion the broad RYA advice is spot on, and as usual Pete 7 is as well concerning the throttle!

I agree but i suppose what should be said that some boats have different transom angles to some can trim in more than others forcing the bow into the water more.

James

[Nos4r2]

Originally Posted by Cookee

Derrick - In my opinion the broad RYA advice is spot on, and as usual Pete 7 is as well concerning the throttle!

Yep.

Personally I find it equates to riding a trailbike fast over fairly rough ground where you'd use your bodyweight to move the C of G as trim, and the throttle in much the same way as on the trailbike. (note-I never did do the fancy 'landing on the front wheel' thing that motoX riders do and it wouldn't work on a boat-I've got 1st hand experience of it )

It's quite easy to demonstrate on a 4m boat as you're less than 1/2 of most wavelengths.

[Nos4r2]

Originally Posted by J S

I agree but i suppose what should be said that some boats have different transom angles to some can trim in more than others forcing the bow into the water more.

James

That's what you use the trim limit pin for.

IMO You shouldn't be able to have the engine trimmed in so far as to have the engine 'leaning backwards' in relation to the keel.

[J S]

Originally Posted by Nos4r2

That's what you use the trim limit pin for.

IMO You shouldn't be able to have the engine trimmed in so far as to have the engine 'leaning backwards' in relation to the keel.

Yes i agree with that. But if someone gets into a boat that isn't set up correctly and thinks its correct to trim all the way down on a certain type of wave and doesn't have that much experience. It could go wrong.

James

[Derrick]

Many thanks to all respondents! I have read right through the thread highlighted by Pete7. I had hoped to attract attention to this question from more of the highly qualified RYA instructors and trainers on the forum.

I can follow the advice to trim up in a following sea this makes good sense and with judicial use of throttles hope not to submarine. What I find more difficult to rationalise is the advice to trim the bow down in a head sea. It may seem that this could set the bow at a disadvantage in two ways,

1......it may tend not to rise quite so readily

2......raising the bow would present the sharp edge of the V section to assist in parting the wall of water ahead.

I appreciate that judicious throttle would be needed too.

Whilst I don't doubt the wisdom of the RYA I would also welcome a commentary on why they give this advice. I am particularly hoping to hear from the RYA folk on here who are probably very familiar with the rationale.

Many thanks in advance.

[martini]

Originally Posted by Derrick

I can follow the advice to trim up in a following sea this makes good sense and with judicial use of throttles hope not to submarine. What I find more difficult to rationalise is the advice to trim the bow down in a head sea. It may seem that this could set the bow at a disadvantage in two ways,

1......it may tend not to rise quite so readily

Derrick, if you think about the weight distribution on most ribs and other planing powerboats, this is never going to be a problem in a head sea. In reality your biggest problem is keeping the bow from pointing at the stars, hence the need to trim down.
With ribs in particular having a tube full of air round the bow giving maybe a ton or so of buoyancy, it would be very unlikely that the bow would try and go through a wave rather than over it.