Permatrims for TomCats

[Bob Cat]

This option wasn't even considered when I got Dive Cat, hull #6 or so. I think there was still some issues with engine hole placement and Armstrong Bracket height at the time.

Since then, I found my economical speed stops at 8 kts and doesn't start again until 22 kts or so. Granted, I had the 300# compressor in the transom (since removed), too.

As you may know, Dive Cat is for sale. I'd love to be able to tell a new owner that trim tabs can be installed to help the performance from 14-22 kts.

Please enlighten.

Bob Cat

[thataway]

We haven't tried the Permitrims yet--and had considered them--but by putting the bow down and getting the boat up on a plane, she will plane down to 16 knots without the Permitrims. This may be due to different engines and mounting. At first I thought that the low 20's were the slowest we could go and still stay on a plane. A bit of playing with the trim has proven me wrong. However, I do have to get down to about 6 knots before I have the same fuel effeceincy as I have at 24 knots. (according to the flow meters).

I suspect if someone had fuel flow numbers before and after Permitrims this would answer the questions. The Glacier Bay people swear by the Permitrims--but this is a displacement boat.

[rogerbum]

John had them put on Tomahawk. As I've only been on his Tomcat in the water, I have nothing to compare to, but with the Permatrim foils on his Honda 150's, the boat planes at about 11-12kts. When we were in the rougher waters and slowed way down, I enjoyed being able to trim the motors all the way down and pushing the bow down.

[gcharlie]

Correct spelling, I think, is Permatrim.

See http://www.permatrimmarine.com/ and http://www.shipyardisland.com/Permatrims.htm .

[Doryman]

I bought a pair and am installing them now. Will report back after I have a chance to try them out. The company I bought them from is very efficient and well-run enterprise. I was impressed by how they handled my order. The Permatrims themselves look very substantial and well-made.

Warren

[drjohn71a]

Hey all.... Several reasons I had the Permatrims installed right out of the barn:

1 - Almost all photos of the TomCats in motion showed the engine were trimmed down alot, prob to the max.

2 - Almost all photos of the TomCats in Planing mode showed a high bow.

3 - The design at the stern shows alot of "loose" water going into those props.

4 - Reading up on the better engine trim options, they all were considered to have an effect similar to increasing hull length.

I wanted all those things!

With the tabs straight out..... not trimmed down to bring the bow down, the TomCat planed, in fairly turbulent waters, from 12-14 Knots with little or none of the feeling like you were climbing out of hole like most planing hulls. I know some of this effect is from the hulls themselves, but I think the tabs help.

Trimming the engines down with the PermaTrims while heading into heavy chop definitely kept the bow down and allowed us to go a bit faster, yet stay comfortable.

The tabs are so large, and there are two of them, so you can feel alot of change in the boat from a small change in the trim.

Also, if you happened to be overboard, trying to get back aboard, without the dive ladder in place, you can easily step up onto the Permatrims for a 'leg up'. Engines off, of course.

John

[thataway]

My experience is that I leave the engines in neutral trim comming up on a plane (No Permitrims). In Deep V's I have had to trim the bow down to get on a plane, but not on the Tom Cat. However John definately describes staying on plane at a lower speed and this is a very good advantage--and probably alone is enough to convince me to buy the permitrims. I work the engine trim a fair amount in rough seas--one hand on the throttle with a finger on the trim, and the other on the wheel.

Generally I have noted that top speed is decreased by a mile or two an hour with tabs on smaller boats. My top speed has definately decreased as I loaded up the boat--so it may not be that inportant.

John is correct that there is a lot of prop wash (rooster tail) comming up. If the Permitrims decrease this--there may be and advantage in effeciency.

My cavitation plates are visiable on the surface when running.

I do bring the bow down with the trim when running into chop--I suspect that the Permitrims will do this faster, perhaps with a little less trim angle.

I had one fuel flow sensor go bad, and want to be sure that I have the calibration correct before switching--I want to compare fuel mileage with and with out Permitrims.

Maybe I can attatch my auxillary light bar directly to the Permitrims (with shock cord)--the Permitrims will stick out further aft than the engines do when trailering (we trailer engines down).
Thanks for the information on your experience.

[drjohn71a]

Bob, Having read about your using a light bar on the engines, I was planning to shock cord it to the Permatrims. They provide quite a large aft platform.

John

[Alok]

I took Top Cat out for an extended run yesterday with Permatrims on. Instead of the usual 2-2.2 mpg at 27 mph, I was getting 1.8 to 2 mpg. Adjusting engine trim did not make any consistent difference in fuel efficiency.

Has anyone else noticed a drop in fuel mileage with Permatrims?

[Sea Wolf]

Alok-

Not having fuel monitors, I've not seen the mileage drop with various hydrofoils, but instead have noticed a mile or two drop in top speed.

It's the same thing, either way, caused by the drag of the water on the foil surfaces.

It's probably minimized when the foil is at a non-tilted angle, more when tilted to trim the boat.

Trim tabs also drag the same way with the same effects.

It's a nice feature, but not without some drawbacks.

Same old story: No free lunch!

Joe.

[katkt]

Permatrims are the Bomb!!!

When I first got our Tomcat, I was bothered by the feeling that it didn't sit level in the water underway. The bow up attitude was tough to over come when running in a chop. you could fix the out of level feel but it required a pretty radical difference of the trim from one motor to the other for results.
This last weekend, I had a chance to try them out in choppy conditions. I've been landlocked for awhile.
The difference was night and day. The boat responds to even slight trim adjustment whether your trying to move the bow up and down and or adjust a list towards the port or starboard.
I was able to force the bow down alot and make running in the chop alot more comfortable.

Now, this is the older 24 and not the newer 255. Althought they are the same hull, they are very different boats do to the brackets, and weight.

Fuel monitering gauges are on my list of things to do, so I can't say much about economy plus or minus. I do know that running with the bimini up and the new "hat bill" would most certainly have an effect on my mileage.
My top end speed seems like it will be about the same. I was trimmed up to the 3/4's mark, and was seeing the speed close to where its been in flat conditions, with the motors trimmed just shy of breaking loose.
The bow comes up nicely when the motors are trimmed up. I'm sure the trims add drag, otherwise they wouldn't work. They do what I want, and until Hugo starts making boats I'm willing to sacrifice some economy to aid handling. I'll plant another tree.

Gordon