Boat and Motor Trim

[sportfish58]

G'day All, Went out to test a mates 5.5m Condor(WA glass company) with a 115HP Yamaha 2 stroke and the Package does not seem to have much Trim.(reference WOT 6000rpm)
Boat sits very flat in the water while travelling.Cruising at 4300 rpm(could not get the speedo to work) from motor full down the spray line out the side of the Hull is close to the middle of the Boat.
When you Trim the motor almost to a rooster tail the spray line only move back about a foot back along the Hull. I checked the motor height(trimmed) and could not see any of the Trim Plate, and only
see the leg joint above it. It has 4 holes in the Trim Plate were a Tab(Dolphin tail type I would guess) would have been at some stage. Would the Trim Tab make that much difference
or could there be other issues. "Your Thoughts on this"
Cheers

[Oceanic Dave]

And how does the motor line up when it is on the trailer? Can you attach any pics? Is the cavitation plate level to the bottom of the hull?

[sportfish58]

And how does the motor line up when it is on the trailer? Can you attach any pics? Is the cavitation plate level to the bottom of the hull?

The cavitation plate is slightly higher than the bottom of the Hull.I am not near the boat to take pics. cheers

[Moonlighter]

If you are saying that at a fast cruise speed, you looked over the back but couldn't see the anti-vent plate (large plate above the prop) because it was totally under water, then the motor is too deep and needs to be lifted higher..

That would also go a fair way towards explaining the lack of response to trim changes.

The ideal is to have that plate just skimming the surface at a decent cruise speed with the engine trimmed out to a normal position. That is really the only way to be sure engine is at the right height, lining it up against the keel is really only a very rough guide to get a starting point, then test at speed and adjust from there.

Also, check the max recommended rev range for that engine - I don't think the 2 stroke is recommended to rev to 6000rpm. Once you get the engine height lifted and set correctly, I suspect you will need a larger pitch prop to get the WOT revs down a bit.

[sportfish58]

If you are saying that at a fast cruise speed, you looked over the back but couldn't see the anti-vent plate (large plate above the prop) because it was totally under water, then the motor is too deep and needs to be lifted higher..

That would also go a fair way towards explaining the lack of response to trim changes.

The ideal is to have that plate just skimming the surface at a decent cruise speed with the engine trimmed out to a normal position. That is really the only way to be sure engine is at the right height, lining it up against the keel is really only a very rough guide to get a starting point, then test at speed and adjust from there.

Also, check the max recommended rev range for that engine - I don't think the 2 stroke is recommended to rev to 6000rpm. Once you get the engine height lifted and set correctly, I suspect you will need a larger pitch prop to get the WOT revs down a bit.

Thanks Moonlighter for your input. Will an aftermarket trim tab help also.Cheers

[ozynorts]

It won't help until you get the motor height right. Once that happens you can play with everything else.

[Moonlighter]

No, do not put a foil on a motor that is set too deep!!

It can cause nasty problems, can dig in when you turn sharply and throw the boat over.

Get the engine height set correctly is the #1 task to do!!! Nothing else wil fix a motor that is set too deep and the problems that this causes.

It isn't hard to lift an engine. Your 115hp is not too big for a DIY job.Here is how we do it, in effect, you are moving the boat and keeping the motor still.

1. Sit boat/trailer on a flat bit of ground. Chock wheels. Disconnected from car.

2. The motor is held on with 4 bolts. Usually, the top bolts go thru a set of holes in the motor bracket, and the lower bolts sit in a slot on the bracket, so you only have to fully remove the top bolts because the bottom ones will slide up or down when loosened.

Get a block of heavy wood like a pine sleeper and lie it flat on the ground under the skeg. With the motor trimmed down so it is vertical, wind the trailer jockey wheel up so the motor moves closer to the ground and its weight becomes supported by the skeg sitting on the block of wood. Don't worry, the skeg is plenty strong enough to take the motors weight.

3. Get a couple of strong mates to hold the engine steady while you remove the top bolts and loosen the bottom ones right off. Really, they just have to keep it balanced, there is not much muscle required, just some care. You might need to jiggle the trim switch a bit to loosen the motor from the transom and the sika that is used on the bolt holes. Clean up the sika around the bolt holes (top and bottom) and the motor bracket. (Sika 291 marine is the one to get).

4. Then go back to the jockey wheel and wind it up a bit so that the transom moves downwards, until the motor bracket lines up with the higher holes you want to use on the motor bracket. Get your mates to tell you when the height is right. You don't have to wind it far.

5. run back around to the motor and slip the top bolts back in, add sika around them (both ends where they enter and leave the transom) to seal the transom holes again, and tighten them up. Once the top bolts are back in and firm, you might need to partially remove the bottom bolts so you can clean off the old sika and put fresh stuff around to seal them up again.

Done. Allow to dry and water test again to check the height.

[sportfish58]

No, do not put a foil on a motor that is set too deep!!

It can cause nasty problems, can dig in when you turn sharply and throw the boat over.

Get the engine height set correctly is the #1 task to do!!! Nothing else wil fix a motor that is set too deep and the problems that this causes.

It isn't hard to lift an engine. Your 115hp is not too big for a DIY job.Here is how we do it, in effect, you are moving the boat and keeping the motor still.

1. Sit boat/trailer on a flat bit of ground. Chock wheels. Disconnected from car.

2. The motor is held on with 4 bolts. Usually, the top bolts go thru a set of holes in the motor bracket, and the lower bolts sit in a slot on the bracket, so you only have to fully remove the top bolts because the bottom ones will slide up or down when loosened.

Get a block of heavy wood like a pine sleeper and lie it flat on the ground under the skeg. With the motor trimmed down so it is vertical, wind the trailer jockey wheel up so the motor moves closer to the ground and its weight becomes supported by the skeg sitting on the block of wood. Don't worry, the skeg is plenty strong enough to take the motors weight.

3. Get a couple of strong mates to hold the engine steady while you remove the top bolts and loosen the bottom ones right off. Really, they just have to keep it balanced, there is not much muscle required, just some care. You might need to jiggle the trim switch a bit to loosen the motor from the transom and the sika that is used on the bolt holes. Clean up the sika around the bolt holes (top and bottom) and the motor bracket. (Sika 291 marine is the one to get).

4. Then go back to the jockey wheel and wind it up a bit so that the transom moves downwards, until the motor bracket lines up with the higher holes you want to use on the motor bracket. Get your mates to tell you when the height is right. You don't have to wind it far.

5. run back around to the motor and slip the top bolts back in, add sika around them (both ends where they enter and leave the transom) to seal the transom holes again, and tighten them up. Once the top bolts are back in and firm, you might need to partially remove the bottom bolts so you can clean off the old sika and put fresh stuff around to seal them up again.

Done. Allow to dry and water test again to check the height.

Thanks again, My own boat I can see the whole Perma Trim tab while cruising. I knew about motor height but didn't realise it could cause these problems if not set in the correct position.cheers

[Fed]

I can't say I've had to experiment with motor heights (just lucky) but from what I understand raising the motor will reduce bow lift.
You might want to run a string line under it in various places and check the hull for hook. (concave area towards the stern)

[Moonlighter]

Thanks again, My own boat I can see the whole Perma Trim tab while cruising. I knew about motor height but didn't realise it could cause these problems if not set in the correct position.cheers

No problems!

Many people don't realise that a motor set too deep will adversely affect the boats "attitude" on the water, it's general handling, can cause porpoising, poor performance, poor fuel economy and lack of response to trim changes.

When they do get the height set right and then, if necessary, sort out the prop size, it can make a marked difference and turn a boat from a sloth into a sports car by comparison. It could, for example, produce a 10% improvement in fuel economy without too much difficulty!

So so it is one of the most important things to get right on your setup. If you can help your mate sort this out it will be well worth the effort.

It may well be that someone attempted to use a foil on the motor to solve these problems previously, not knowing that they were treating the symptoms rather than solving the real problem. So put any thoughts about adding a foil out of mind until you have the engine height set correctly.

Good luck and let us know how it goes.

[Cloud_9]

as a rule of thumb the cav plate needs to be at least 1" above the rear of the boat. reason being the the water leaving the hull of the boat rises 1" for 1 foot distance from the back of the hull at planning speed. hence the reason for the 1" up.
depending on the boat my seafarer is in the second top hole and that's still just a tad low and my cav plate is just under the water .
I also have a trim fin on the boat to no determent. but that said it does impact top end speed a little
but having the motor a little deep was the normal custom and practice .
make the boat a little more stable but will reduce the total trim a little too.
prop type will also be affected by how high you go too, if you have a pusher or more load style prop it will cavitate on a higher setting.
and would require down trim for a tight turn at pace.

[Fed]

What motor you running Cloud?
I have a Viking the same as yours with a V4 90 HP Evinrude and it's a little unresponsive to trim. (No foil)