Poor Engine Trim - Help.

[thomas]

I took my RIB out today, well the Mrs drove, and once we got onto the plane there is a lot of water shooting directly up, I've tried to capture it in the photo but not very well, it's kinda like a curtain, I've tried with and without wings but there seems do be no difference, I'm sure someone will know straight away but I'm very new to small boats and have no idea, but wondered if it was something to do with the angle of the engine.

The RIB is a 4.5m Valiant with a Selva 50hp 4 stroke.

[Poly]

I think it will be engine height and/or trim angle. What height is the anti ventilation plate relative to the bottom of the keel? A photo taken from the transom looking towards the prop would be good (be careful sitting there and if there is any risk you might fall/slip consider adding a second kill cord).

[Courageous]

Is there an obstruction at the bottom of the hull, maybe a sounder transducer? My transducer flings up like this a bit though perhaps not quite as bad.

[thomas]

I had thought that the leg might not be long enough but trusted that it was done properly, does this look a little short?

[Poly]

That engine is the correct length. I would raise it an inch or so and see if it improves things. Is it Power Trim or Manual?

[thomas]

it's power, on the throttle lever - how would I raise it?

[jambo]

Originally Posted by thomas

it's power, on the throttle lever - how would I raise it?

Hi like Neil I think your plate is to low and it needs to come up a little. Hope you find the answer.

J

[Poly]

It depends if your engine is bolted or clamped (or both!) on.

Exactly how you do it will depend on how much muscle you have available as well. Very simply:

- balance / support the engine. ** Beware that lump probably weighs more than me and is an awkward shape**
- unbolt / loosen the engine
- either lift the engine or lift the front of the trailer to drop the transom
- refasten the boat to boat (if it is bolted you can probably do this without drilling any holes)

NORMALLY the starting point is to have the bottom of the keel level with the antiventilation plate - as highlighted in yellow here.

BUT if you are new to all this then perhaps play with the trim angle first to see if you can eliminate it without the spanners. The preferred trim depends on lots of things (speed, load, waves etc) and should be tweaked as you go.

[jambo]

Having a second look at it and I maybe wrong as I sometimes is! Is the angle of the OB rather severe as against the transom as it does seem a little at an angle would have thought the plate and the keel should be more towards the parallel.
Just a thought.

J

[thomas]

I can move it up quite easily as it's bolted on and there are lots of holes in the mounting plate to adjust, but I guess you lot knew that.

It's hard for me to play with the trim as I can't get the Mrs, who said "what on earth do we want one of those for" out of the healm seat.

[m3mm0s rib]

From the photo it appears that the motor has the correct height. If not there is POWER trim you can buy an after market and to solve any problems

[Poly]

Would be worth you and the Mrs getting some training (RYA PB2) which will teach you what those buttons are for! If as a total beginner she had the engine trimmed all the way down I'd start there. Search the forum for advice on trimming.

[Hightower]

In addition to what Polwarts said. Using black marker, mark a line on the transom before you raise. That way you can drop it to the original position and have a referance mark when lifting. The other thing that might help you, if you have to take out bolts to move engine up, is to clap wood on the transom either side of the saddle to prevent it from moving/slipping sideways.

[thomas]

Thanks Polwart, yesterday was the first time we really has it out, I had asked her to trim it up a little but she was not 100% confident where the trim was and as we were not going very fast I figured it best to let her enjoy herself, I did manage to get it level at one point but it didn't make any difference.

We're not really beginners, we had a Fairline Targa 30 for many years and use a friends 10m Raider a fair bit so quite used to trimming legs and tabs on those but she was never really interested in healming big boats unless they have sails, this is very different and she loves it so will be doing her PB L2 with her friend pretty soon. I am having to learn about small boats and as this one was not rigged properly I have a fair bit to learn.

Back on topic, I've raised it up which has left an inch between the transom and the bracket, do I need to support this or will the 4 bolts be enough?

[skippermarky]

Hi Thomas, that looks better, just about write, it may be a fraction high, try it before you do any permanant work on the transom, what i would do is cut a piece of hard wood to go between engine bracket and transom, temporaraly fixed with the dredded silicon, a nice firm fit that way it will support the engine weight, you obviously know the principles of trimming, so now its just practice, good luck regards Mark

[BogMonster]

The spray is definitely the engine being too low, my Humber did it at any speed unless trimmed well out, you got a "rooster tail" of water out the stern, just trimmed out until it disappears. The engine was a DIY rig by the first owner and I think it was an inch or two lower than it should have been.

In some ways I actually preferred having the engine a bit low and trimming out, the Osprey is set "correctly" and when there is no weight in the back of the boat (and me in the front) it ventilates too easily on turns for my liking.

[Poly]

Steven, do you trim down for tight turns?

[Dirk Diggler]

Originally Posted by skippermarky

Hi Thomas, that looks better, just about write, it may be a fraction high,

Still looks to low to me!

[jyasaki]

Thomas; you can have the wife try this:

Run at a given throttle seeting (something near flat out, but not crazy-scary-fast.) Note the speed on GPS. Have the wife trim the motor out in half-second bursts without changing throttle, and see what happens to speed. Keep this up until the motor is trimmed up high enough to start slipping a bit. Drop it back down a touch, and you'll have figured out what the effects of trim are.

My normal throttle up is to nail the throttle open until the boat climbs out of the hole and begins to plane, then I trim up about a third or so while reducing throtttle to get to the speed I want. I then adjust trim to get the ride I want over swell or chop. Should note that my prop usually starts to slip when trimmed about 2/3 to 3/4 up when on plane.

jky

[Courageous]

"Thomas; you can have the wife........" Extremely generous offer! Me next!