The OFFICIAL TomCat Permatrim BEFORE AND AFTER thread!!

C

Captain Starbucks

Member
I wanted to lower my planing speed as much as possible. I operate almost entirely in the ocean in the PNW and conditions aren't always favorable for using the TomCat's legs. I knew at the end of last year, I was either going for new stern lifting props, or Permatrims, or both. After several conversations with Ken at PropGods, he talked me into trying the Permatrims first, and I'm sure glad I did.

Anyways, last fall prior to storing for winter maintenance, I thought I'd get some baseline data. To be perfectly clear, the conditions before and after weren't identical but I'll try to line out the differences as much as possible (noted in the image below).

I'm a bit suspect of the GPH figure on the With Permatrim side at the 4,000 rpm point. I'll have to double check that next time I'm out.

A few things of note: The boat was 300 lbs or maybe more lighter on the With Permatrim side. Also, the water had a slight ripple on it on the With Permatrim side. Ripple has a great drag reduction factor, ask any floatplane pilot.

Permatrim_snip.sized.png
 
Thank you and interesting take. I had a 2006, TC 255, with the Suzuki 150s. Stern lifting props (4blade), SS. I also added the Permatrims to attempt lower the planing speed, and cruising speed in semi displacement mode. I don't remember doing as an exhaustive analysis on the RPM/Speed, fuel consumption. (My impression was that the fuel gauge/flow meters were not that consistent--I was pulling data off the turbine type of gasoline flow meters, not the engine computers.

My impression was that the Permatrims threw a bunch of water up, on the sides/at speeds in the 9 to 10 knot range, Almost to the point I considered it possibly dangerous.

I also got lower high end speed, and decreased fuel use at the higher speeds. What makes your fuel/speed somewhat "suspect" (not being disrespectful, but wondering if other factors were in play????). Because most folks who use Permatrims find that the higher end they have a slightly increased drag and slightly raise the fuel consumption--many have found that they cannot achieve the same high end speed at WOT. (My WOT were at 6,000 RPM and very close to what yours are at 5700 RPM, which is exactly where you want to be with the Suzuki (Different gearing and using considerably greater pitch props--my recollection was I was running 21" pitch props. I had two sets one at 19 the other at 21. I rarely got over 2 mpg. An exception was where I ran almost 200 miles at a constant speed "Best efficiency" run. I am sure my boat was heavier than yours, with extra batteries, Honda Generator, full fuel tanks, full water tanks, etc.

So I am interested in if you sustain these numbers over longer distances, and longer periods of time, running two ways over the same course--distance, etc. I understand that GPS will give us numbers without having to use a measured mile--but GPS gives us speed by position and can be different that speed thru the water. This is why I like to use a measured mile, both ways. to get my most accurate mile.

I don't know if you were using the engine computer for "mileage" or an external Lawrence, like I was using. How did you determine you had 18 or 17 gallons of fuel in each tank? That is just to "pat" a number.i??

There are just so many variables.

Again, Thanks
 
I ditched my permatrims on my tomcat. I don't notice much of a difference. I'd be interested in adding a foil wing between the hulls aft to create lift....if there was such a thing off the shelf.
 
Cap' Starbucks,
Are the fuel consumption figures in your chart for 2 engines? My Tomcat 255 with Suzuki 150s displays between 1.9 - 2.2 GPH when cruising between 18-21 mph, but I'm thinking the electronic display is reading just 1 motor...What say you --
 
A number of us who have owned the T om Cat 255 have talked about increasing performance. (The 2.0 S miles/gallon) is reasonable for both engines, and running at a moderate speed. I averaged 2 S M/Gal in the run from Apalachicola to Pensacola about to 200 niles.

A foil would definitely be a possibility, but there are a number of issues--all of which could be resolved. Especially if a new boat was built with the beefed stress points.

If serious I would consult with Morrelli & Melvin who are located in Newport Beach, Ca. They would be some of the best in the World in predicting the effect and costs. They have developed and converted a number of boat (both sail and power) to more modern propulsion, faster speeds, and better rides.
 
nwboater":2vborz99 said:
Cap' Starbucks,
Are the fuel consumption figures in your chart for 2 engines? My Tomcat 255 with Suzuki 150s displays between 1.9 - 2.2 GPH when cruising between 18-21 mph, but I'm thinking the electronic display is reading just 1 motor...What say you --
Click to expand...

Yes sir. My fuel burn figures I posted in the charts above reflect fuel burn totals for both engines based on the factory installed 2009 era Yamaha digital gauges.
 
After cancelling two offshore trips this year, I finally got a chance to run the boat in the ocean this weekend. We did about 90 miles on Friday, and about 50 miles on Saturday.

Water conditions were our typical "north-south-easter" which is generally lumpy.

Swell was 5 feet at 11 seconds forecast and observed out of the west
Secondary swell was forecast and observed 2 feet at about 8 seconds out of the SSW
Wind speed was 12-14, occasional whitecaps, occasionally 5-10 mph, chop usually less than 1 foot. Again, just lumpy bumpy.

The biggest benefit of the Permatrims was to bury the bow at slowest possible speed, which was about 11-14 mph and being able to stay on top as much as possible without coming off plane. Fuel economy was poor, but about .3-.5 MPG better than without Permatrims in lumpy conditions. As Bob and a few others have noticed, they may not benefit the fair weather operation as much in the TomCat, but for those of you who venture far into the ocean in less than perfect conditions will benefit greatly from the addition of these relatively inexpensive Permatrims.

At slow speed in lumpy conditions with the bow down, the engines will be churning up a lot of frothy water. I highly recommend all engine cowl seals and throttle/electrical feedthrough be coated generously with high viscosity silicone grease. This will do a great job at keeping the water out. I was shocked my engines had zero evidence of water intrusion.

Anyway, it's not often these days when I try a new-to-me product and walk away feeling like I got my money's worth, but this was a solid win for my use case.

Rob
 
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