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Old 01 April 2004, 15:47   #1
Country: UK
Make: Ribcraft
Length: 4.8m
Engine: Mercury F60 EFI
Join Date: Dec 2003
Posts: 89
How does trim work?

Hi everyone,

Having had a recent problem with trim (Teething Problems thread) I now want expand my knowledge of PTT. When on the plane, trim out to push more of the hull clear of the water, resulting in faster speeds. This is as far as my knowledge goes as yet. (I would be guessing if I suggested anything else - When not on the plane, trim in so boat gets on the plane faster?) So, with a view to experimenting this weekend, can anyone offer any more uses of trim...


Robert1 is offline   Reply With Quote
Old 01 April 2004, 16:17   #2
Country: UK - England
Town: Torbay
Boat name: Marlin
Make: PBS humber 5.5
Length: 5m +
Engine: 115 optimax!!
Join Date: Jul 2003
Posts: 351
trim can also be used when driving in rougher weather - trim in when going into a head sea, this lets steep v of the bow punch through the waves and trim out when in a following sea to stop the nose stuffing.

All good in theory, not quite that staight forward in practice

This is however, not always a set ofhard and fast rules, different boat lengths, wave heights and wave spacings may require different actions

Colin F is offline   Reply With Quote
Old 01 April 2004, 16:47   #3
Country: UK - England
Town: Midlands
Make: Nautique
Length: 6m +
Engine: PCM 5.7l
Join Date: Oct 2003
Posts: 1,082
Ok, to begin with you will trim all the way in, this pins the bow down and also gives the stern some lift over the bow wave when getting on the plane.

Once on the plane the sea conditions will determine how you trim the boat. When you trim out its not to lift the bow so much as to get the prop driving the boat forward and not a) pinning the bow down or b) pinning the stern down.

If your driving in chop then you will most likely keep the bow pinned down most of the time, in sharp turns you also want to be trimmed in all the way.

For out and out top speed you can watch the spedo and trim out all the way untill the speed stops rising, i ran my old boat up lake windermere like this and the bow is so light and airy you wouldnt think about doing it anywhere except mill pond flat water.

In most conditions you would trim untill the engine is square to the boat, trimmign out further reduces the wetted length but compromises the way the hull works.(Cos its scimming along on about a foot of hull)
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Old 01 April 2004, 18:38   #4
Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 5,416
Originally posted by simmons0
in sharp turns you also want to be trimmed in all the way.
Do you?

Maybe aye, maybe no.
jwalker is offline   Reply With Quote
Old 01 April 2004, 21:22   #5
Country: UK - England
Town: Margate / Ramsgate
Boat name: Bumbl
Make: Scorpion
Length: 8m +
Engine: Yanmar diesel
Join Date: Feb 2002
Posts: 2,837
I find triming out 1 tiny flick of the switch greatly reduces vibrations - i presume it's as simple as moving the engine out a fraction so it's not touching the end stops, this must surely decrease wear on all the components and the boat as a whole.

I try and do this even before getting / going onto the plane.

I'd be interested if anyone else finds this true, i've never noticed it on a boat before.
Daniel is offline   Reply With Quote
Old 02 April 2004, 00:45   #6
Country: UK - England
Boat name: none
Make: bombard sib
Length: 3m +
Engine: petrol 15/3.5
Join Date: Oct 2003
Posts: 402
Yes,I get that,trim in all the way and there is a vibration through the boat,I thought maybe the engine was so far in it touched the hull but tried it on the trailer and its nowhere near.
I have only been out once so far but hope to get out at the weekend to play with trim,I have read that to give a softer ride,you should trim out.certainly trimming out increases the speed by quite a healthy margin.

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