Permatrim

I finally got out on the water today. The new permatrim works great in getting the stern up out of the water on take off. It also works well in pushing the bow down in choppy seas and smooths out the ride. I still had to use the trim tabs to level out side to side tilt.
This was the 1st time out since last Sept. so it will take a few trips to get the "goody" from the pt. but the two mentioned items were immediately obvious.
I was cruising at 3500 rpm's, 18.5 mph and 7 gph. I kicked it up to 4000 rpm's. 22.5 mph and 9 gph.
We did catch 6 halibut and two king salmon while out. That was a big plus.
 
Removed my Permatrim today and reinstalled the Whales tail I had previously. I wanted more bow down so installed a permatrim like I had on our 22, didn't get the anticapated result. Less top end and decreased fuel economy so backtracked. What I plan on doing is extending my trim tabs in hopes I'll be able to achieve better bow down performance and not blow out the trim tab cylinders. BTW have single 150 Verado.
 
I've had my Whale tale for a year now, I already had trim tabs. The advantage for this device is choppy water, yes you lose 1 1/2 or so of speed how ever your boat no longer Bangs thru the chop, our C Dorys have a sharp bow and when you force it down it just cuts right thru. It's a night and day difference, you'll become accustomed to trimming the bow down once you enter chop. You'll notice the speed loss and trim it back up but theres that banging again so you trim back down and she cuts thru like a knife thru cake. Your trim tabs will be your port starboard trim and your permatrim will bring the bow up and down.
It's like sailing, with my sailing background it came to me quickly just reflex. If you don't have feelings about boat trim it my be annoying.
 
For those who can measure fuel usage, I'm really interested in how the permatrim affects it. We travel moderately loaded, and while the extra ability to get the bow down in a chop would be nice, it would be really REALLY cool to see an extra couple points of fuel efficiency.

The range extending powers of slightly better fuel economy would be awesome.
 
brevity":cwrbcq0w said:
For those who can measure fuel usage, I'm really interested in how the permatrim affects it. We travel moderately loaded, and while the extra ability to get the bow down in a chop would be nice, it would be really REALLY cool to see an extra couple points of fuel efficiency.

The range extending powers of slightly better fuel economy would be awesome.
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There are lots of variables. For example you can plane at a lower speed. But my general impression (backed by some fuel flow numbers in the C Dory25 and Tom Cat 255, is that there is minimal top end speed loss, and perhaps a slightly lower fuel economy, but you have to have a fuel flow meter to validate that. The best range extender is go go slow. (displacement speeds--5 to 6 knots.

One variable which always needs to be looked at--with or without a foil on the motor antiventillation plate, is the position of the motor on the transom. If it is too deep, then your "mileage" will decrease.

Beausaw--what do you mean by "blowing out the trim tab cylinders?
My experience is that the Permitrims are better than the "Doelfin" foils, but I have not tried the "whale tale" Why is the "Whale Tale" better than the Permitrim?
 
thataway":1q04f7t6 said:
Beausaw--what do you mean by "blowing out the trim tab cylinders?
My experience is that the Permitrims are better than the "Doelfin" foils, but I have not tried the "whale tale" Why is the "Whale Tale" better than the Permitrim?
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I wouldn't say the whale tale is any better then the Permitrim only that it did not significantly improve ýbow down characteristics of my 25, and I experienced about 2 to 3 mph reduction in speed at WAT.
So the way I see it I'll have to improve the characteristics of the trim tabs, perhaps by welding or bolting on a2 or 3 inch extension. Or perhaps place a block between the cylinder foot and trim tab so that they will extend further. Now all this his theory but it's my belief that I will see better bow down capability with more robust trim tabs then just the addition of a Permitrim.
Additionally when trim is not required in calm water I won't suffer fuel economy by the additional drag of the Permitrim, the whale tale is thin stainless steel and doesn't appear to induce extra drag.
Now I know that for the Permitrim to perform optimally it needs to run at the surface so the engine would need to be adjusted up on the transom this would require a lot of additional experimentation when the end result may not be significant.
I'm not sure if the trim tab cylinders can handle the addition of more surface area or the stress of over extending the trim tab. I don't have a problem if the tabs don't totally retract because at even high speed I usually have a little tab extended and this doesn't seem to affect speed, in fact it keeps the boat from porpoising.
 
On my boat the tabs are normally about 60-80% extended most of the time (according to the tab position display). The boat is normally aft loaded with gas/batteries/motor/one person in the cockpit. We don't use the water tank usually and there is not much stuff in the berth area.

The motor is usually trimmed all the way down (in).

In rougher water the tabs get extended more, sometimes all the way, to get the nose down far enough for a smoother ride.

In my situation a Permatrim might help some. The drag from adding the permatrim will probably be offset by requiring less tab angle, so the change in fuel mileage is probably a wash.
 
Jay,
Thanks for your thoughts. If the Permitrim (or Whale Tale) is not running on the surface, it tends to increase drag more. The motor should be set so that the anti ventilation plate sits right on the surface when running. If the plate is running on the surface, it makes little difference as to the thickness of the metal. Not that hard to look at the engine, when on a plane on calm water. (Of course an adjustable jack plate is the best way to determine exactly where the engine belongs--but not necessary or practical in the C Dory 25. Plus jack plates set the engine back further, and make a whole other set of dynamic issues.)

The question is raised does the fin alone cause drag to the extent of loss of speed, or is it the effect that the fin has on the trim of the boat. I would argue that most is the effect of the trim is the major factor. I did a lot of playing around with fuel flow and attitude on the 25.

Definitely you need to consult with the manufacture of the tabs. I don't know if you had Lenco, Bennett, or Boat Leveler tabs (I have all 3 on my own C Dories). Generally Tabman (Bennett) will tell you how much more tab extension (that is putting on a longer plate or wider plate) will be allowed without damage to the cylinders. I personally would not add area, with out consulting the manufacture.

Generally I use the tabs to trim the boat side to side, and to an extent less to push the bow down.

I am a bit concerned by your statement about porpoising. The boats should not porpoise. The 25 is inherently a stable hull design, and the only evidence I have seen of instability, is either exceeding the 30 knot speed limit (and this is not constant), or trimming the bow down excessively--and that is more in the way of bow steering or broaching--not porpoising.
Porpoising is a very complex subject, but it implies that there is a serious imbalance on the boat, or deformity of the hull (hook of the aft planing surface is most common). You should not have to have any trim tab when running…

Several discussions of porpoising: (The first one is more what we have with the C Dorys, and that is weight distribution. The second more for high speed boats, where it is a very dangerous issue--and perhaps the dynamics are different between the two)

http://continuouswave.com/ubb/Forum4/HTML/005556.html

http://www.boatdesign.net/forums/boat-d ... -9509.html

Hard to know exactly what is going on, without ridding in the boat, or watching it from along side to see. I had the 22 with no tab or foil. My 25 came with trim tabs, and I added the Permitrim, and was able to compare the difference--which was enough to make the ride far more comfortable.
Of course a lot depends on how the boat is loaded and balanced. The current 22 has Lenco tabs, and a Doel Fin (When I first got the boat there were no Permitrims in the country for the Honda 90--so I just never got around to changing it out--and I will).
 
On my 22 Cruiser with both Permatrims on twin Honda 40s and trim-tabs, on a 600 mile cruise I discovered less speed/efficiency loss trimming with the motors v. trimming with the tabs.

The tabs when lowered definitely increase drag, dropping speed, raising fuel-burn, so no matter the objective - running level, trimming bow-down for to-weather chop or bow-up for running with it - I trim first with the motors, then if more trim effort is desired, I use the tabs. Mostly I run with tabs pulled up all the way to reduce both displacement and wetted surface drag.

With modern electronic chart-plotters giving speed-through-water and speed-over-ground readouts, it's easy to see which has the greatest effect on efficiency in real-time. In practice, the only time I need to use any trim-tab is when I really need to press the bow down for head-seas when tanks are full, or when weight is concentrated considerably on one side or the other.
 
brooks&judy"..... The tabs when lowered definitely increase drag said:
The other tool, which gives a lot of information, is to have fuel flow meters, and sometimes we get surprises.

Sort of overlapping two threads which are going --the other being the weight in the stern--there are times when boat owners do have to give a not more trim (and it hurts efficiency), is when loaded heavily in the stern, and when at altitude, where you loose 3% hp for each 1000 foot of elevation. In that case, trim tabs become a necessity for more efficient running at certain speeds.
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Just brought up a 1984 27' cruiser/commercial fishing boat (of its day) with a Volvo penta 110 turbo charged. Have some questions if anyone would care to let me know if they too have a like year and model?
 
QueenBEA,
Welcome Aboard.

You probably want to start your own threat. Go to Home, click "Forums", then General Discussion, "new topic". Put your topic in there. If you want to know now many 27's you can go to the "our C Dory", and click on "Model"

There are a number of 27's--many have converted from the Diesel to outboards. Great boats!
 
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