Permatrim Hydrofoils

So, is anyone running both tabs (Lenco) and a Permatrim? Would
you recommend both, or can you achieve everything with the tabs
that the Permatrim provides?

Mike
 
Mike: Depends on how you use your boat and how much weight you carry. I started with the Perma-Trim because it was cheaper and easier to install than the tabs. It works as advertised and would recommend it. It holds water around the prop for better prop grip on the water in all situations. When you are going slow and bobbing over big rollers this helps. Tabs don't do this. Most other foils won't either. The Permatrim starts working as soon as you put the engine in gear. Then as speed increases it works even better as more water flows under it. It can induce drag if you trim the motor all the way down as will the trim tabs. Any engine angle below parallel starts to add drag.

I don't feel the tabs begin to work until the speed is about 12 mph and up. I carry lots of weight aft and it is not feasible to move it forward into the v-birth. This causes the stern to ride in a hole with the boat running up hill. I then added Bennett M120 sportabs. They help in lowering the bow. They are great at balancing the boat side to side. The Permatrim cannot do this. I felt with the kicker that M120 tabs would be a tight fit. Now that I have ran them I wish I had even bigger tabs for greater lift with less drag. These tabs as well as the Permatrim have the ability to really reach down deep in the water at a steep angle. This will lift the stern and force the bow down, but it also can add much drag that pulls down engine power, boat speed and economy if too much down force is used.. If a bigger tab was used it would not have to be pushed as far down in the water to produce the same amount of lift. Hopefully creating less drag and keeping your speed and economy up.

Lastly I run a yamaha 80 h.p. which is a heavy detuned 100h.p. I feel that a 115h.p. with a Permatrim would really help my boat's attitude at all speeds. Turning a bigger prop with more torque can only help.
 
OK, thanks. I'll wait and see if we sit in the hole much. This past season
we didn't but we had just bought the boat and it was very lightly loaded.

I've been adding weight all winter :-) But, most has not been in the stern.

Mike
 
Mike:

Forgot to mention in those running shots in my album. I had just unloaded all the camping gear, coolers, one dog and spouse to shore. Up front was a fully serviced porta-john, a 5 gallon water jug and a 20 lb river anchor. So there was more weight up front compared to the back. 20 gal water tank was full as was the fuel tanks and an 80 lb German Shepherd. She got sick after a few high speed handling maneuvers. :oops: The kicker is a 15 h.p. Under sink is full of food and kitchen utensils.

Basically the stern is about as light as it gets except for fuel burn. So when I load her down she really settles in the rear when under way. It has always seemed to me like the prop digs a hole in the water and the stern settles down in. More power/bigger prop here would help. A 15 pitch prop gives me 5200 rpm. I can go to 6000 rpm. So I am looking for a 14 pitch prop for more power at cruise rpm. The propulse adjustable for my engine adjusts from 16 - 20 pitch so that is of no help.

The Permatrim is installed but not the trim tabs in the photos. The Permatrim does a good job of both lifting the bow when needed and lowering it in the chop. I found that when going up the back of 5 - 6 foot smooth swells the prop grips uphill and with the bow high the boat falls off the backside very smooth like. Maintaining a fairly level ride without dropping nose down. Great exciting ride. I feel the permatrim helps in holding the boat up on the downside with no prop slip in this situation.

So as not to sound like an advertisement for Permatrim. The tabs where added for more lift. The bigger the better. When I first got them I thought they where big. Now that I have used them it doesn't take much tab at all to balance from left to right. And they are fantastic at this. But it does take a big tab to lift the stern without causing uneccessary drag. That is why I wished for bigger tabs. I just bought a canoe for a dink. I just need to get a mount put together. If it works out, the nose will rest on the bow rail to leave room for the bimini top. This forward weight should help the stern.

If I didn't carry the weight I wouldn't need both but as you can see with the canoe the weight just keeps coming on. (maybe it's a subliminal plan to get a CD-25). But I do carry weight, have both Permatrim and tabs and find they work well together. :thup
 
Could not tell from prior posts if anyone was using twin Permatrims - Does anyone run Permatrims on Twin Hondas on a CD22? If so can you adjust the angle of each engine to get the port to starboard balance that most adjust with trim tabs."

Also - I have read here that in a following sea you want the trim tabs up. - how does that apply to Permatrims - is there any danger issue to Permatrims in certain sea conditions that trim tabs would help?

Thanks

Jim on Endurance
 
jstates":ty5snzb5 said:
Could not tell from prior posts if anyone was using twin Permatrims - Does anyone run Permatrims on Twin Hondas on a CD22? If so can you adjust the angle of each engine to get the port to starboard balance that most adjust with trim tabs."

You can use two engines with Permatrims to trim a boat, but the separation of the motors is not as great as the trim tabs, and more trim angle is needed for the same effect for lateral trim. Differential trim like that on the motors will usually be less efficient than trim tabs, effecting gas mileage.

Also - I have read here that in a following sea you want the trim tabs up. - how does that apply to Permatrims - is there any danger issue to Permatrims in certain sea conditions that trim tabs would help?


You'd get much the same effect on the Permatrims being lifted by a wave approaching from the rear that you would with trim tabs. With trim tabs, they can be raised up pretty much out of the way. The motor trim can be done similarly, but now you're affecting thrust angle, too. You certainly don't want both of them down in a following sea with appreciable wave height. The trim tabs won't cancel out any bad lift from the Permatrims. Putting them down to do so is in the wrong direction and compounds the problem. A lot depends on your boat loading and, of course, the sea state and your skill level. If you want them both, try it out. If they lift too much in your conditions and the ride gets really squirley, you have to give something up, probably the Permatrims.

Some folks who have them both say that Permatrims are not necessary or beneficial once you have trim tabs, and it's nice to be able to trim the boat with the tabs and use the motor to adjust the thrust angle for efficiency and gas mileage w/o overtrimming the boat!
Click to expand...

Joe.
 
Joe,

I am guessing that you do not have Permatrims on your CD. We were in about as rough a following sea as one could survive with our Permatrims and there was never a risk of the Permitrims lifting the stern to the point of overpowering the bow flotation on these C-Dory designs. The Permatrims don't float, you know. That bouncy bow design of the C-Dories seems to keep the bow clean pretty well as long as one does not overload the forward area.

I think the Permatrims allow much better directional stability and more highly controlled, quick movements and adjustments when you're in the rough stuff.

Trim tabs don't give you the directional stability and control that the Permatrims do, and Permatrims on close dual engines won't level the boat like trim tabs do. Soooooo, why not both?

John

John
 
John-

I do have a hydrofoil on my main motor, but not trim tabs. I was basing my comments on what others have said in the many discussions over the years. I get limited opportunities to experience the heavy seas conditions where I boat. Is it possible your observations are somewhat unique to the TC 255 experience? Did you find a way to add trim tabs to your TC-255? Thanks for the comments!

Joe.
 
Hey, Joe...

Well, I don't see much need for trim tabs on the TomCat, considering how well the widely spaced Permatrims work. On top of that, there is very little room at the end of the hulls and a very complicated flow pattern back there.

We had waves going over the entire boat, base winds 35K gusting to over 50K so I think that is as wild a ride as I'll ever accidentally get into again. Downsea, the Permatrims caused no problems, and I feel they helped us position ourselves better and more rapidly than a bare hull.

the bow never dipped to the point of submersion.

John
 
John-

Sounds like the Permatrims are quite the ticket on the TomCat 255!

I started to look up some of the older discussions of "Permatrims, trim tabs, and following seas" with the Search engine, but it came up with 1735 thread topics on 35 pages, and probably 40-50,000 posts! To many to research for anything less than a Ph.D dissertation!

The Search engine needs to be capable of searching within it's own results sequentially, or something. Perhaps one of the computer gurus to help us out on understanding how to use it more effectively?

Someone had a suggestion on how it could be improved about a month ago.

Joe.
 
I'll throw in my 2 cents worth on this subject. We have had the Permatrims on the Mary Ellen with twin 40HP Hondas for about two years. I am very happy with the setup. It gives me the port to starboard adjustment I wanted. I do not have to use much trim to level the boat out. It also helps with the bow attitude. I am not even considering putting trim tabs on after installing the Pematrims. They were very easy to install and are very nicely made. I looked at the Honda SST Hydrofoil made for this engine and did not like them. They seemed very cheap in appearance. I have not experienced any adverse handling problems in bad seas. As you can tell I am a big fan of Permatrims, they were a great addition at a fair price.
 
This is a very informative thread. I take it there are no issues with your motor's factory warranty from drilling holes and adding this non-factory modification. I'm getting a new 90 Suzuki next month an wouldn't want to do anything to mess up that nice 6 year coverage.
 
Jim, My understanding is that it won't effect the Honda warranty OTHER than any damage to the area upon which it is bolted. I have heard you could remove the Permatrims and fill in the holes down the line, if you wanted.

Joe, et al, re: the possibility of waves lifting the stern and dowsing the bow - I think the trim tabs may be more likely to do that since there is no space between them and the hull, so any wave action is captive. The Permatrims have quite a large space between them and the hull, so maybe that allows some of the wave force to dissipate and escape significant bow down pressure.

John
 
John-

You bring up an excellent point!

I'm going to have to do some thinking about this over time.

I'm not sure we 100% understand what's going on with trim tabs and hydrofoils in following seas.

Is the problem that the flat surfaces are acted upon by the motion of moving water in the wave which uses the tab/foil as a lever to turn the boat (just like the hydrofoils act as a lever (as well as increasing planing area) in making the boat act like it's longer and therefore ride smoother, or

Is it because the tab/foil at the rear of the boat acting as a lever fulcrum pinned in the water restricts the ability of the bow to rise over the wave motion there and leads to the boat being unable to properly respond to the waves which leads toward broaching, or

Are both of the above operating? or

Are there other forces or consequences operating?

If you stop a minute and look at the traditional dory concept, you'll notice that the stern is tapered a lot. This is probably to minimize the surface area exposed to a following wave and reduce the force that the wave could have on the boat. The same principle is used on double-ended sail boats. It's kind of like having a wave-breaking bow on both ends. Those double-enders are slow, but they don't broach! (Of ccourse, part of this is attributable to a heavy keel.)

Well, if the above paragraph of theory is true, then modifying the C-Dory hull to a square transom to both mount an outboard and promote planing with a square cut-off hull- is both a good and bad idea in that it makes for convenience and faster boat performance, but bad in that it makes the boat vulnerable to following seas.

So maybe the tabs and/or the foils are an exaggeration of the trend away from a more seaworthy pointed or narrow stern, and/or a restriction limiting the ability of the boat to respond to the wave motion.

One method I often use to figure out things in physics and mechanics is to exaggerate parts of the problem, as it allows one to see/understand things more clearly in the exaggerated form. Following this process, round out the hull until it is completely circular, like a buoy. Now does the wave motion apply any twisting or restrictive motion to the round hull? Put a long lever on the buoy with a big flat paddle like blade on it. Now what happens when a wave strikes the new combination from different anges? (As a side thought- can a sailboat or powerboat have TOO BIG a rudder that can trip the boat when exposed to wave action?)

What do you all think?

OK, who's going to be the first to build a double ended style extension around their stern to correct all of this?

Joe.
 
Wow.... lots of heavy thinking for so early in the am, Joe.

What I was afraid of was the possiblilty of breaking waves driving the stern down in rough seas. I can't say whether this happened or not during the storm I was in, since the adrenalin was pumping and my attention was so strongly focused on port, starboard and forward.

The only untoward boat behavior I noticed was, that when the winds gusted to 50 plus k, the bow was going downwind no matter what else you did at that moment. So, I tried to set up a course over correction in advance of each gust.

John
 
John-

I'm thinking that if you go fast enough down-wave (away from the wave motion), the wave motion from the rear doesn't catch up to you.

This means that you could use trim down from tabs or hydrofoils to negotiate cutting through waves without getting caught from behind. At least until you HAVE to slow down, then it's back to raise the tabs/foils.

You and Roger were probably going so fast with the wind at your back that you were much more likely to go over a wave and fall down its front than be caught from behind.

Perhaps the two narrow cat hulls are less vulnerable to waves from behind, too (assuming the hulls only, but the Armostrong Brackets at displacement speeds probably square the hull back to monohull conditions.)

It would be interesting to think about whether a displacement cat or a planing cat or an in-between type hull would do better in these conditions. Bob Austin probably knows!

Joe.
 
The storm Roger and I were in was not nearly as bad as this one that my son and I had gone thru the day before we met up with Roger. I think the winds were 25 gusting to 35 when Roger an I were out... a bit foggy now... maybe he'll remember. Most of the time things were well under control at those lower wind speeds.

John
 
A comment about trim bow down (either trim tabs or fins on the cavitation plate). The major problem is not really the fins or tabs interacting with the wave aft--but with the bow being depressed and causing the bow to be pushed down, causing bow steering and the possiblity of a broach.

When running in heavy weather with waves from behind, one prefers to get on the back of a wave, and stay there, rather than getting into the risky situation of being pushed down the front of a wave. If you were to get in this position, you can bring the bow up--probably more rapidly with either trim tabs or the Permatrims.

I don't see any problem with the permatrims going down wind and seas, as long as one is cautious. With the cat, there is less risk of bow steering than of stuffing the bow in a wave as you come down the front side at an acellerated speed.

Going to the Glacier Bay's which do not handle as well as the Tom Cat down wave/seas, the Permatrims do not seem to be detrimental. In fact there are a number of reports that the Glacier Bay's handle better in following and quartering seas with the Permatrims than with a single Doelfin (outside) on each engine or without a fin.

My Permatrims have been shipped and the weather is beautiful, so when they arrive, we will test them and I'll report.
 
drjohn71a":1jvxr340 said:
The storm Roger and I were in was not nearly as bad as this one that my son and I had gone thru the day before we met up with Roger. I think the winds were 25 gusting to 35 when Roger an I were out... a bit foggy now... maybe he'll remember. Most of the time things were well under control at those lower wind speeds.

John
Click to expand...

Your memory seems about right too me. The weather was a bit nasty while we were out and there was one section there while we were headed north that was particularly bad - had to slow down to 7-9kts. However, I don't think we had much more than 25kt winds most of the time. Still, the quality of the ride in the Tomcat makes me want to get one.
 
The major problem is not really the fins or tabs interacting with the wave aft--but with the bow being depressed and causing the bow to be pushed down, causing bow steering and the possiblity of a broach.
Click to expand...

Having trim tabs on my 22 and having piloted following seas on the Pacific outside Neah Bay running at up to 9 feet 7 seconds, I can tell you I never run with trib tabs down in a following sea. Why? Because another time at Neah in only 6 foot waves every 12 seconds I did so and the boat unexpectedly and within 1 second cut sharply to the right (approx 60 degrees). Thataway is correct - the biggest risk with running trim tabs in a following sea is radical and rapid loss of steerage. Not only does everything on the boat want to go off the outboard side when this happens (inlcuding people), the boat is turned into the trough where it can broach via the next wave. Add to this the fact that "bow down" is never the way you want to slide down the front of a wave which, depending on your speed and the speed of the following sea does happen.

Believe me, you do not want to do this.
 
Back
Top