Motor height vs. permatrim

[serpa4]

Finally installed my permatrim on my Venture 26 with 200hp Suzuki.
Didn't realize any difference. MPG seemed down a tad.
On my Suzuki, there are two sets of horizontal fins. The lower on is obvious the anti-ventilation plate. About 2.5 inches above it there is a 2nd smaller rib, but it still protrudes about 1.5 inches and is fairly flat.
The 2nd higher on is about where my engine is in the water at 25mph.

Is my motor too low? If the anti-ventilation plate is riding the surface of the water, isn't the propeller about to come out of the water at the slightest wave, bump? Cant props suck in air from the surface also if its too close.

If it doesn't do much in that I don't notice it, then it might as well come off and get my mpg back. I have trim tabs also.

My searching on the internet always turns up pictures of deep V boats and their anti-V plates are like 1/3 way down the transom V that is in the water. I.e. if they draft 18" water, then the plate is about 9" below the water line when sitting level. Haven't seen (yet) a video of a boat on plane.

 

[thataway]

You want the anti ventilation plat just under the surface of the water. Usually this is about "level" with the bottom of. the C Dory/Venture. The Permatrim should be just on the surface of the water.

It sounds as if your motor is too low==maybe even two holes too low--but go up one.

What is your WOT RPM, and Boat speed? You will get very little decrease in speed or MPG--but it can be measured. The permatrim allow you to get your bow way down when going into chop, and that gives a much better ride. Trim the motor up for going down waves/wind. You will probably plane at a slightly lower speed.

 

[serpa4]

You want the anti ventilation plat just under the surface of the water. Usually this is about "level" with the bottom of. the C Dory/Venture. The Permatrim should be just on the surface of the water.

It sounds as if your motor is too low==maybe even two holes too low--but go up one.

What is your WOT RPM, and Boat speed? You will get very little decrease in speed or MPG--but it can be measured. The permatrim allow you to get your bow way down when going into chop, and that gives a much better ride. Trim the motor up for going down waves/wind. You will probably plane at a slightly lower speed.

I have to see if I need to raise the motor a hole or two. I have thee sets of fins on the outboard. Now I'm thinking I need to verify what one is parallel with the water. I definitely know its not the bottom one..the actual anti-V plate. I need to see if its the next one up or the one above it. There is about 2 inches between each.

I don't know the WOT RMP. I've run over 30mph and think its about 5,000 at 30mph. I know there is more left, just have not gone over 30mph. Guess I need more data and a picture of my anti-V plate while underway at 20mph. I usually cruise at 18-25mph. If I'm chasing MPG, then I can drop to about 16 and I'm definitely into the 3+mpg range.

I may make a Bahama run this weekend. I'll check then.


"What is your WOT RPM, and Boat speed? You will get very little decrease in speed or MPG--but it can be measured. The permatrim allow you to get your bow way down when going into chop, and that gives a much better ride. Trim the motor up for going down waves/wind. You will probably plane at a slightly lower speed."

I'm amazed how slow I can go and be on plane. I think I can run about 15mph, maybe less. Doesn't seem to be much of a transition.

 

[thataway]

The first question we often ask is: "What is your Wide open throttle RPM and speed." implied with this is "is your boat trimmed or the best possible speed for the condition." "Are you lugging the engine, or not achieving the best speed for the RPM"

The ant-ventilation plate is the first plate one above the prop, and contains the trim tab. This should run just under the surface of the water, and the Permatirm should be mounted right above this on just on the surface of the water.

The anti-ventilation plate should be from 1/2" to level with the bottom of the boat. Depending on type of hull--the deep v (in the 20's dead rise) would be the deepest motor. Since our C Dorys/Ventures, have extremely low dead rise, the anti-ventilation would be right at the same level. I have tried my boats to have the Permatrim right at the surface of the water--no cavitation-depending on the hull type. For example , my other boat is an 18' Center console Catamaran. It has a skeg like projection I the tunnel, to help to direct the flow of the water coming out between the hulls. Single engine cats are notorious for blowing out--because of this skeg like appendage)-a properly set up Caracal Cat has this minimized. Going down wind / waves, I will occasionally have some cavitation, For this reason, ideally I should have a remotely operated jack plat installed. (I don't have one.)

 

[serpa4]

Measurements say my anticavitation plate is about 1 or 1.5 inches higher than the bottom of the hull. Both are level with a bubble gauge.

 

[NORO LIM]

Serpa4, just to make sure everybody is on the same page here. When you are assessing the depth of the Pematrim below the surface of the water, are you talking about while the boat is on plane? That is definitely what you need to check. The Permatrim should be right at the surface (maybe a slight film of water running over it) when the boat is on plane. Obviously, it takes at least two people to check this - unless you are completely reckless and willing to leave the helm while the boat is planing!

 

[serpa4]

Serpa4, just to make sure everybody is on the same page here. When you are assessing the depth of the Pematrim below the surface of the water, are you talking about while the boat is on plane? That is definitely what you need to check. The Permatrim should be right at the surface (maybe a slight film of water running over it) when the boat is on plane. Obviously, it takes at least two people to check this - unless you are completely reckless and willing to leave the helm while the boat is planing!

While I was on plane, I couldn't see the permatrim. I assume it was several inches under the water. I"ll have to look again to verify. But sitting on the trailer, the permatrim is about 1.5 inches above the bottom of the hull..
Given those two conditions, you would think that the water at 20mph coming off the bottom of the hull would make the permatrim out of the water while on plane. But it's not. Now... the water is not overly clear and there is a lot of foam also, so this weekend I'll be down in the keys with clear water and my wife so I'll look for the permatrim while at 20mph. Usually my cruising speed is about 18-20.

 

[NORO LIM]

. . .

While I was on plane, I couldn't see the permatrim. . . . But sitting on the trailer, the permatrim is about 1.5 inches above the bottom of the hull..
. . .

Very puzzling. You are right - you would think the Permatrim would be at the surface when the boat is on plane.

 

[thataway]

. . .

While I was on plane, I couldn't see the permatrim. . . . But sitting on the trailer, the permatrim is about 1.5 inches above the bottom of the hull..
. . .

Very puzzling. You are right - you would think the Permatrim would be at the surface when the boat is on plane.

If the Permatrim is 1.5" above the bottom of the boat (depending on trim, both when measured and when on plane, I would expect you might not see it. Ours ran with just a little water over it. There is not enough square surface area to have the boat lift as it would on a foil. (Ie foiling craft--Cats, monohull add sailboats.