Trim setting volvo outdrives.

msimms

msimms

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Just interested in what value you trim to, and do you find it makes much difference to the attitude of the boat.

If the conditions are a choppy/rough and we're down to 18-20 knots I leave the legs right down at -5. I've experimented and found that if I trim out the bow rises and need to drop the tabs to present a better attitude. As this doesn't seem to improve speed or increase comfort I gave up and just leave the legs in and add some tab to counter any list.

In more favourably condition where we can cruise between 21-27 knots I set the legs to 2. Values of 0 thru to 5 don't seem to make that much difference, any lower and the boat tends to list to one side or the other - feels a bit like it's out of balance. Once the leg is set to 0 or above it feels in balance and then only needs a little tab to counter any wind induced list.

Cheers

Mark
 
Think you're on the right approach. MBM did feature about 12 months ago called 'attitude' I think. Await details on forum or search.
Your boat will always react slightly different to other boats / engine combo's. i.e. we are full planing, 5.5tons flybridge with twin 200 hp on A5 duo props.
Do also remember that the leg counter calibration can be re-set and adjusted very easily and whats right for you may be different numbers. We are -3 when fully tucked in but one drive will show -4 sometimes.
Best way we found was get a constant sea and wind track, level revs, level attitude, check speed log and then adjust leg a little. Wait a few seconds and see if speed alters. Proceed a little more and check again. With a more lumpy sea when we want more nose in we trim down bow further by tucking legs right in and full tabs.
Anyway we found for ours last weekend at about plus 3 we gained about 2 knots against tucked right in - which meant we could reduce revs to maintain an easy 25 knots cruise increasing good economy even further !.
For marina manouvering or vectoring etc we found tucked right in seems perhaps best. Good luck but its mainly trial and error.
 
My S27 with KAD 44s went from -2 to +7 (max allowable under high power).
For getting on the plane, trimmed right in to -2, tabs down.
Normal cruising at about 23-25 kts, trimmed to about +2, trim tabs right up.
Flat out in calm water 37kts (GPS and speedo, no current) trimmed at +7.
Bear in mind that you will lose a couple of knots for being in the Med.
 
I am constantly amazed by how the number of folks that don't understand how to use the trim to get the best from their boat, last week I was out on an SeaRay 25 with a V8 and also an Aquador with a Kad 32, and both owners were amazed that I could get so many more knots out of their boat. The SeaRay guy was considering having me pull the motor, so I suggested a seatrial first, I usually say nothing and just observe their driving habits, he put both trim flaps full down and wondered why he couldn't get more than 26 knots, needless to say he was over the moon when he saw it go past 35 knots and sit better on the water, and the Aquador man wanted me to change the turbo as he was convinced it was the reason for poor performance, while he left the leg full down and trimmed with the flaps!
It really is a weakness on the part of the dealer or seller not to explain how the systems work, I always ask the customer if they understand the trim functions even at the risk of them being a bit offended.
Thefatlady has it right, the reason some boats have a difference at - trim is there are different transom angles that are used by the manufacturers which will have a bearing on how far the drive tucks in at full down, a correctly calibrated drive will read 0 when the cavitation plate is exactly inline with the keel, obviously most planing boats have a measure of bow rise when planing so if you leave it at 0 the prop will be pushing slightly downwards, by trimming out you ensure the prop is as near to vertical in the water as poss, this will vary with conditions and load but you get the gist.
Often you will see a discrepancy of a degree or two on a twin installation, but this is down to slack in the system.
 
Re: Trim setting Volvo out drives.

the best thing to do is go and play with them, but when you do an adjustment give the boat time to settle, watch the speedo, if trimmed correctly your speed will increase, then let it settle , try another adjustment ,let it settle, etc when over trimmed it will reduce speed. remember that every sea condition may require a slightly different setting, same for weight on the boat and wind, so go and play /forums/images/graemlins/grin.gif
 
agree it's amazing,a nd sad, how many haven't a clue - but there are just so many things to vary!

for smaller boats hull speed is a major factor to - especially in the 10 - 20 knots range.

then there's engine power curves.............. /forums/images/graemlins/laugh.gif

playing with GC1s Cranchi I prefered 0 heading into a chop and +2 with it whilst Pete was convinced that it was 'slamming' and preferred -4 into the chop. Basically to me that was forcing the bows down 'through' the sea when allowing the bow to rise a little with the waves was actually softer but did carry more 'motion' - it certainly never slammed ie it was completely soundless! He definitely preferred the solid feeling that trimming in gives - I prefer the feeling of release that efficient trimming gives. Neither is right or wrong in one sense - although I would suggest I would get more miles to a tank.............. /forums/images/graemlins/laugh.gif
 
I doubt whether I am getting the best out of my trim but I try!

My boat is 10m, deep vee, 5 tonnes, twin AD41s, duoprops with a trim range of -7 to + something.

What I have found works best is:

to get onto the plane: -3/-4

max speed on flattish water: -1/0 (I get 34 knots clean, currently down to about 31. Revs up to 3600)

into wind and waves: -4 or more

displacement speed: -2 to -4

All of the above is with both tabs fully up or one down only to the extent necessary to counteract the effect of cross wind over the deck.
 
I think you have it pretty well nailed looking at your figures, it definitely pays to experiment and get to know your boat as you have done.
 
In theory....

Anything you stick in the water creates drag, so it's not suprising that trimming the leg out and then putting the tabs down doesn't help. It's more likely to hinder.

In the first instance I would try running with the tabs no lower than flush with the hull lines. Trim the leg in to accellerate onto the plane, then trim out in small degrees for speed and efficiency. You will soon know what is right for your boat in normal conditions.

Apply small amount of leeward tab to level her up in a cross wind.

If heavily laden or tanked up (or fouled) you could use tabs to lift her on the plane, but back them off as far as you can once cruising.

The only reason for cruising with tabs down in good conditions would be if you found that the correct trim was only acheived with the leg fully in, and better efficiency was achieved with a little tab to allow the leg to be trimmed out closer to horizontal.

When trimming bows down or up for heavy weather the argument for applying tabs arises if they allow you to maintain a slow speed whilst staying on the plane AND staying in control.
 
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