Bigger Cav Plates

[Ozy]

I had a porpoising problem with my new boat and after raising the motor a few holes, shifting weight around etc I had no joy but after talking to a few different hull and prop manufacturers and on the recommendation of my engine manufacturer that I try a Permatrim my boat is performing like it should .

I was lucky enough to find a used Permatrim to suit my motor that had only been on an engine for a couple of runs (thanks Bill) because otherwise I would've had to wait two weeks until more could be made. Garry Turner from Permatrim told me that he couldn't keep up to the demand for my particular model and I had the same comment from Solas about props and thier own brand of foil called a Laserfoil for my model motor.

So my question is if products like Permatrims do such a great job and I know they do because I have had two now, why don't outboard manufacturers make the cav plates bigger?

The Permatrim not only stopped the porpoising but there is little or no bow rise getting onto the plane and it turns and rides so much better .

Edited January 10, 2005 by Ozy

[Bashir]

I guess it could be made as an option for the outboard, that would be most ideal. That way so long as the dealer knows the boats he is selling can tell you whether you need an engine with a big cav plate or not. My boat rides fine without a foil so a bigger cav plate may wreck the performance. Personally I don't think it will ever happen.

[Grantm]

I would say the reason is that not all boats porpoise. It is not the fault of the motor but the fault of the boat/motor combo. Your outboard fitted to another hull probably wont porpoise therefore there is no reason to change the design.

Its a common confusion that the motor is the fault, because it is the motor we modify to fix the fault.

Some motor to boat combinations just seem to fight eachother. Why? who knows.

The problem seems more evident in v-punts over 4 meters with decent size motors than with any other boat. Hornets have the same drama.

A commen fix for Hornets is to change the height of the motor to rectify porpoising, so it does'nt surprise me that when you altered the height, you got a problem.

I see Permatrim's as a last resort, and should not really be used until your sure your boat is set up right. Even then I dont like it. As far as I know they were originally designed to get a boat up on the plane quickly, good for skiers etc. Only in recent times do they seem to be used to cover up boat set up problems.

Its good that your boat now rides well, so I suppose they do have a place, and im sure many people will attest to their rectifying many issues.

Why did you change the motor height anyway ? was there a problem ?

[aussiebasser]

I think you'd find that if outboard manufacturers made the cav plate bigger on motors, they'd break fairly easily. The legs are cast alloy. I have heard of a cav plate cracking because of a foil, but I'm not sure the driver of the boat knew how to use the trim button.

As far as foils correcting porpoising problems, I don't subscribe to that theory. My hornet has a permatrim on it, and at full noise and full trim the permatrim is over an inch out of the water, so it does nothing. They are an excellent device for three main reasons.

The boat will plane at a lower speed, and not bury the bum on take off.

The boat will hold plane at a lower speed, and not bury the bum when slowing up.

The foil assists in making the boat more stable at rest lengthwise. (Cut a piece of ply wood the same size as a foil and try to move it up and down under water, and you'll see why they help)

[Ozy]

I know all boats don't porpoise but a bigger cav plate would assist in the other benefits such as Aussiebasser and I mentioned.

Thanks,

Ozy.

[Ozy]

Hi Ozy,

I had a Permatrim (or similar brand) on my motor and it performed like a dog.

Wacko.

26722[/snapback]

I know guys that have had the foils that look like bat wing and go out to the side and have done nothing, the Permatrims go out rearwards and that is where they come into thier own.

I didn't mean to have cav plates equivalent to the size of foils or the permatrim but just a bit bigger than they are.

Points taken, thanks guys, this has stirred up quite a few around the forums.

Edited January 12, 2005 by Ozy

[Guest Big-Banana]

Ive got a Permatrim fitting to my 7m Plated Aluminium and without it, its handledmuch worse in comparison. Plane is immediate, turning is much smoother and with a following sea is much more comfortable to drive. Cant complain about top speeds as 45knots is enough.