Can I remove outboard trim plate ?

[Dave_S]

Originally Posted by Kastaway

My thinking is that if you just cut off enough of the ventilation plate to give you the 3 degrees that you are looking for it would finish up being very close to the back of the well. i.e. where the shortened plate finished the bottom of the hull would take over. It would also leave enough material to re-fix a flat plate if everything went south or if you wanted to re-purpose the engine for a different application in the future. Nice shiny new bit to be cutting up, I can see it now.....big breath, no turning back now - hoping that you don't find out that it's filled with oil and springs and an important looking flux capacitor. What could possibly go wrong!!

Hahahaha, yep something's wrong in the world the day I'll sit down with a cut-off blade in my angle grinder and go all Mad Max on it, but the day is coming.

[Kastaway]

I know - crazy right, it's almost like the manufacturer expected that someone would fit it to a transom.

[Dave_S]

Originally Posted by PaulvR

I agree, leave it, it is a useful trim tab and often the anode.
I notice in your pic though that you leave your outboard in the water! This is the easiest way to ruin an outboard, as growth in the water intake (as you see) will eventually cut off sufficient cooling water, and it will seize.

Leave the tab, and tilt the motor up, always except at a busy dingy dock.

Nope, t!he image is taken looking up. The motor pulls straight up on slides and is clear of the water when parked and when sailing, this is all about closing off the hole in the bottom of the hull to reduce drag and add a lot of bouyancy.

[Kastaway]

Thinwaters probably right - I'm going to be looking for your future post headed..... "Is Devcon ok to glue ventalation plate back on to outboard ?"

[Dave_S]

Originally Posted by ggray

Well, saildrives don't have an anti-cavitation plate, and what he wants to do is more akin to a saildrive, so it may not be a problem. I say "may not" because the water in the well does have a free surface, but the water may be deep enough to preclude cavitation.

The well will be sealed off when the motor is down and up. I agree, I think it is a non-issue.

[Dave_S]

Originally Posted by Boatyarddog

Yes you can, but only the minimum to get the clearance you want.
In a motor well, your still not very deep.

How is the hole smaller if you cut?
Are you looking to tilt it for draft issues or to make the well opening smaller?
Or, just to be able to get the lower end thru the well hole?
There may be a better way.

There maybe cavitation, in waves.
Sail drives are so deep there's not really wave issues that deep.

I would limit the cut to the middle of the trim tab zinc, as the some of the uptake is in that plastic screen.
And, I'd consult a breakdown of the lower end first.
Boatyarddog

I'm going to fit a cover over that big hole in the hull, through that cover plate I'll just make a hole 15mm bigger that the silhouette of the leg. I will probably cut it just level with the back of the trim tab. When the leg is down a plate attached further up the leg will come down and blank the hole. When the leg is up I'll have a door that swings down and seals it and a self bailer to drain the well.

But yes, I will find out what's in there first.

[Dave_S]

Originally Posted by thinwater

So, we think that plate is there because the manufacture had extra aluminum to get rid of? Every manufacturer? For the last 75 years? Odd.

Yep, they are all Mad

It's for a bit of a uniquely different application. As above.

[Cadence]

JMHO, I believe you would lose more than you would gain. Just because the leg is below the hull doesn't mean you can't draw air through the hole in the hull to cause cavitation. A bundle of money goes into the design.

[MicHughV]

Seeing as that cavitation plate is located inside that hole underneath the hull, I don't see where cutting it off (or trimming it to fit) should cause a problem. That plate is really there to stop the prop drawing in air from the surface, but seeing as the prop is inside that hole, there is little chance of that happening. I would not cut it off, but trim to fit.

That other little plate right above the prop, is there to trim the thrust from the propellor, so that the motor will run straight. It's generally set by the manufacturer to ensure this.

[AKA-None]

If I may ask what is the cost to replace the entire outboard?
That plus your time is the worst case scenario for this experiment
YMMV

[Boatyarddog]

Originally Posted by Dave_S

I'm going to fit a cover over that big hole in the hull, through that cover plate I'll just make a hole 15mm bigger that the silhouette of the leg. I will probably cut it just level with the back of the trim tab. When the leg is down a plate attached further up the leg will come down and blank the hole. When the leg is up I'll have a door that swings down and seals it and a self bailer to drain the well.

But yes, I will find out what's in there first.

Maybe you could fabricate a rubber shield that could clamp around the OB " neck" and lay at water level, clipping to spaced attachment points along the boats well.
Rubber would allow for movement R to L, if left a bit loose.
And, should limit the amount of air available to allow for any cavitation.
Just a thought.
Boatyarddog

[thinwater]

The well will NOT be sealed well enough to prevent ventilation. I've seen air pull down tip-rudder cassettes, and I seriously doubt the fit will be that good.

A fence will not work at water level. It needs to be well-submersed (see image).

The fix? My boat needs an anti-ventilation plate on the rudder. Otherwise the rudder ventilates above ~ 12 knots (a motor will ventilate standing still). This was designed by the architect, Ian Farrier.

Sail Delmarva: Rudder Rebuild and Adding a Fence

[Boatyarddog]

Originally Posted by thinwater

The well will NOT be sealed well enough to prevent ventilation. I've seen air pull down tip-rudder cassettes, and I seriously doubt the fit will be that good.

A fence will not work at water level. It needs to be well-submersed (see image).

The fix? My boat needs an anti-ventilation plate on the rudder. Otherwise the rudder ventilates above ~ 12 knots (a motor will ventilate standing still). This was designed by the architect, Ian Farrier.

Sail Delmarva: Rudder Rebuild and Adding a Fence

Not sure how this article relates to the OB, cavitation, "ventilation" issue here.
Could you elaborate how this would work?
Seems a good way to keep water around your rudder, but?
Pretty sure the OP, doesn't want to Compleatly eliminate the cav. plate, just wants to trim it a bit.
Boatyarddog

[thinwater]

Originally Posted by Boatyarddog

Not sure how this article relates to the OB, cavitation, "ventilation" issue here.
Could you elaborate how this would work?
Seems a good way to keep water around your rudder, but?
Pretty sure the OP, doesn't want to Completely eliminate the cav. plate, just wants to trim it a bit.
Boatyarddog

It does not relate directly, but indirectly in several ways:

• Adding something at the surface of the water will not work. Too many gaps, too turbulent.
• A cover that fits around the outboard may not work. This rudder cassette has quite a tight fit with the hull, including spacers, and still it sucks air down. The pressure differential of an outboard is probably greater than that on a rudder.

He can certainly experiment. But he may loose some power, and most critically, he may loose some power in up-and-down conditions (rough weather). He just needs to be aware of the seriousness of the risk. Those plates are not there for looks, they are there because EVERY manufacturer considers them critical.

[Boatyarddog]

Originally Posted by thinwater

It does not relate directly, but indirectly in several ways:

• Adding something at the surface of the water will not work. Too many gaps, too turbulent.
• A cover that fits around the outboard may not work. This rudder cassette has quite a tight fit with the hull, including spacers, and still it sucks air down. The pressure differential of an outboard is probably greater than that on a rudder.

He can certainly experiment. But he may loose some power, and most critically, he may loose some power in up-and-down conditions (rough weather). He just needs to be aware of the seriousness of the risk. Those plates are not there for looks, they are there because EVERY manufacturer considers them critical.

Humm.. Guess he won't know till he tries, there seems to be no conclusive answer here.
Maybe we All with learn from this, keep your fingers crossed.
Haven't seen to many OBs that don't Cav. in bouncy conditions.
Boatyarddog