Permatrim Hydrofoils

[Da Nag]

I needed more lift when loaded heavy, so I went to add a hydrofoil. Had an SE300 that worked fine on the Yamaha F80 on Da Nag 19, but I just didn't like the way it mounted to the Honda BF90 - the pre-drilled holes in the fin would require me drilling too close to the adjustment skeg for comfort. Picked up another model locally - a WhaleTail XL. Same problem...

I know both of them could be mounted - the C-Lou's have the SE300 on their BF90. Jon's just much more confident in his drilling skills than I am...

So...I took a chance on another model - Permatrim. Here's a link to the manufacturer's page, and here's one for the guy that sells them in the US. The BF90 takes the large model ($104).

This hydrofoil is relatively new to the US, but has been used for many years down under with lot's of happy customers. The main difference between it and the others I've seen - it's built like a tank, and fastened more securely than the others - five bolts per side instead of two. The manufacturer claims it's sturdy enough to use as a swim step - I believe them, but I think I'll stick with the one I've got. Oh - and it looks cool...

I installed it last week, and took it out today for the first time with a rather heavy load - four adults, full water, and about 25-30 gallons of fuel. Had plenty of lift, and no strange behaviour in turns. On my CD19, the SE300 had plenty of lift, but never felt quite right in the turns; hard to describe, but it just didn't cut very well. The fin kept the boat a little too level in turns. There are a lot's of differences between the two boats, so I can't say the CD22 would behave the same, but the fin design is definitely different. The SE300 was arched and wide, the Permatrim is flatter and narrow, but longer. They look like they have about the same amount of surface area; there might be a bit more on the Permatrim.

Two pics in the photo album, starting here.

On edit...

Here's how I installed it - the Permatrim came with instructions, but the following worked better for me:

- Lay the Permatrim in place on the cavitation plate, and figure out your bolt spread. On my Honda BF90, it was a nice even and easy 12", so the 5 bolts were 3" apart.

- Take a piece of blue painters tape about 4" longer than your bolt spread, and gently lay it on a smooth surface - glass works great. Roll up the ends so you can remove it later.

- Do the math, and evenly mark one edge of the tape with tick marks for the number of bolts you use.

- Make a couple tick marks on the bottom of your ventialtion/cavitation plate 3/4" in. Using these marks, afix the tape template made earlier so it's 3/4" in, with the front/back bolt tick marks on the tape where you want them on the cavitation plate.

- Take a sharp center punch, and slide it up to the edge of the tape on each tick mark - make the punch.

- Drill all the pilot holes (1/8"). I only drilled the ventilation plate - I didn't clamp the hydrofoil on at this point. Reason being, I didn't have a lot of faith the clamp would hold things perfectly while drilling all 10 holes.

- Clamp and align the hydrofoil. Drill the rear two pilot holes in the hydrofoil using the existing holes in the ventilation plate as guides, then drill the rear two holes with the final bit (1/4") all the way through both the cavitation plate and the Permatrim.

- Bolt up the rear two holes to hold things in place, then finish drilling the remaining holes.

- It's probably a good idea to use some 4200, not only in the holes, but between the Permatrim and cavitation plate.

The above may be overkill, but it gives a perfectly aligned hydrofoil with evenly spaced bolts.

[Chuck S]

The shape looks more like a trim tab than a hydrofoil. There's no wing shape to it like the SST, etc.

What's it do to top speed?

-- Chuck

[Da Nag]

[SeaSpray]

Bill,
I just went back and looked at your pic's again. I am curious about what the permafoil does for the boat that the trim tabs won't do?

I will be getting a CD22 from EQ at the end of August and we are going to do a 3 week cruise in the islands. I am still making choices about what to get on the boat and what to wait and put on later ( after I save more $$'s).

I am also interested in your choices of electronics and windlass.
Do you have a 12v lighter output?

I am also getting the camper canvas - probably the same as yours. Did you get bug screens with yours? I didn't see them in the pics.

I live in Brentwood, not far from Pleasant Hill. It would be a help if we could talk or get together and look at your boat. I am trying to make the best chices before it is too late for Less to make changes.
Thanks,
Steve
W 925-294-2654
H 925-634-0150

[Jon - CLou]

I agree with Bill on the Seasport SE300. The main reason I got it was for lowering the bow in a chop and it works well for that. Turning and lateral movement just doesn't feel right. The boat turns alot better without the hydrofoil and seems to ride better running in a straight line without it also. I'll keep it on for now because I really like running in a two foot chop at about 13 knots without any slap.

[Da Nag]

Seabran Steve - check your PM's. Be glad to take you out on the boat this coming weekend.

[Da Nag]

Well...I'm gonna call the Permatrim and Comprop combination a big success.

Seabran Steve and I took Da Nag out of Pittsburg last Friday - head up the river to Locke for some lunch and back. Had a chance to put things through some differing situations, and the boat handled beautifully in all of them. It wasn't a slouch prior to the upgrades, but the difference was very noticeable.

On the way up river, we had a decent wind behind us (probably 12-15MPH), heading into the current. Small chop, a few whitecaps. It was an incredibly smooth ride, much better than I've had in these conditions before - we pretty much held 12-13 knots with no problem.

Rounding the corner out of Rio Vista, we got into some nice glassy protected areas. Got a chance to open her up - with two adults, almost full fuel and full water, we were just under 29MPH by the GPS, again heading against the current. From the looks of things when we docked, I'm guessing the current was about 2MPH. RPM's were perfect - 5800-5900 with everything trimmed up just right. The most surprising part about the high speed stuff - the handling improvement. I was cranking the boat around hard at 20MPH+, and it was tracking like it was on rails - no sliding in the back whatsoever. I couldn't get the prop to wash out. I'm not sure whether this improvement has more to do with the Permatrim or the Compprop, but with no hydrofoil and the stock Honda 3-blade prop, things were very different. With that setup, turns were predictable at high speed, but it wasn't real tough to get the rear end sliding around. These aren't exactly conditions most of us put our boats through, but it was nice to feel the improvement anyway.

On the way back - those afternoon Delta winds and waves were in our face the whole way back. Water breaking onto the cabin and into the cockpit. We had to slow down quite a bit, but even at 8-9 knots, things were better than usual. Again, much smoother than I've experienced in similar conditions with the stock setup; I could easily keep the bow down at these lower speeds, and the porpoising and pounding was minimal.

At around $200, this is one of the better "bang for the buck" upgrades I've done...

[Jon - CLou]

I sure would like some input from anyone that uses a permatrim and has been through big following seas. That's a concern to me if I get caught in big water, too much lift. Not fun because it feels like you're going to do a face plant in the bottom of a trough.

I read all of Da Nag's and the factories feedback. It sounds like these things work better than any other on the market but haven't heard any reports on lift during following seas.

The Seasport 300 has gotta go.

Jon

[TyBoo]

Jon, I got some things to say on this, but most of it I couldn't say without cussin' a little, so I sent you a PM. But what I remember about the hydrofoil I tried on the TyBoo22 (Doel Fin) was that it was weird. The boat tracked and turned OK, but after a hard turn in one direction I had to oversteer back the other way to get it to level back out laterally. Kind of like riding on a single ski. Didn't like it one bit. Maybe the dorky looking square thing you're asking bout now will work differently.

TTT (Think Trim Tabs)

Note on Edit: Bill, you big sensitive baby, I ain't making fun of your PortaTrim fin by saying it looks dorky. Admit it - it does. That, however, does not reflect on its efficiency or value. I mean, sheesh, you're about the dorkiest looking guy on the CBs, and also the most valuable. If you like having that dorky looking thing hanging back there, then more power to you. (Which you'll need, because anytime you trim the motor out of optimal to force the hull, you're wasting power.)

[Jon - CLou]

Thank goodness for PM's. Mike, I like your thinking, trim tabs are probably the way to go if I don't have to much re-work to do on the stern. I'll save some more pennies and do the tabs first if I can and see what happens.

Jon

[Sawdust]

you knew I couldn't keep my mouth shut. If it works for you - cool. But I'll let some braver soul check that sucker out in a heavy following sea -- such as Jon and I must fish in if we want to be where the slabs are. Even the little toys we use for lift make me shiver and shake when I've got my nose buried in the trough and have white water breaking over the sterm as I ski down the Alpine slope. Different strokes, eh? Our loverly little CD's are just like any other flat butt boat in a following sea -- spooky at best, and adding additional lift aft seems okay as long as you have enough weight back there to compensate... lets give it a good test! Jon, your first

Dusty the coward

[Jon - CLou]

Dusty, the 3 buck Chuck must be getting to me. I don't know what I was thinking. I gotta go with the trim tabs first. Tyboo Mike and I had a little talk and I'm to chicken to put that big piece of plywood on the back of my motor. I know once I have it on, I'll be complaining about lateral movement anyhow. Sometimes I forget where I fish, you know!

Jon

[TyBoo]

Don't you just hate it when someone feels they have to have their conversations privately instead of on the forum where everyone, including the poster, can benefit from the feedback? Sorry. The thing is, you see, there has been a lot of discussion lately about my running total of posts, so I have been trying to limit myself. Well, now it looks like my friend PatA will never catch me!

Here's my thinking on this. (Oh damn - here he goes!)

Bill's stroke is too short. If them Lenco actuators would shove them tabs down deeper in the water, he would not need anything else. I have the same problem on the TyBoo. I added a spacer between the bottom of the ram and the tab to get them deeper, but that leaves me unable to fully retract them to above the level of the hull. On the heay butted CD25, it doesn't hurt anything. But on the light, nimble and lithe CD22, that could be a problem when the water slaps the back.

Now I'm no engineer - in fact, I've never even been to the front of the train nor have I been driving a boat for very long - but I got this theory based entirely on observations from trying both a hydrofoil and tabs (although not together). The hydrofoil acts more to lift the stern out of the water and allow the bow to go down. The tabs act more to push the bow down without raising the stern out of the water as much. Can't prove it, nor am I inclined to debate it with anyone. But it sure seems like it to me. It also seems to me that as little draft as the CD22 has, it would be a good idea to keep most of it in the water at the stern.

The tabs I put on the TyBoo22 were Bennett M120 Sport Tabs. I wouldn't be surprised if the guy who designed them had a C-Dory 22. They are perfect. I never used all that they could do, and when they were full up, they had little effect. But they do have hydraulics, and the simplicity of the Lenco electric screw jacks made me decide on them for the next boat. If I get real ambitious this winter, I am thinking about putting the old Bennett pump and actuators that the Lencos replaced back on to work the Lenco tabs. (And hey - that would give me some cool screw jacks to use when I do the reversible passenger seat. Hmmm....one to move the seat back, and one to fold the table in half. I'll have to think about that some more.)

Another advantage of the tabs over the hydrofoil is not having to trim the motor out of ideal to control the hull attitude. There is an optimum spot for the angle of the prop to be relative to the water surface and the direction of boat travel. With tabs, I was able to find a sweet spot at cruise in the CD22 where the GPS speed would increase significantly with no change in motor RPM, and have a noticeable change in sound that said the motor was not working as hard. It was real fun to play with, and it has to help the fuel economy.

Bill's configuration is great for him and the way his boat is rigged. I am not suggesting that he change it, because if it works, it's perfect. All I am saying is if Jon needs to do something, then the first choice should be the tabs.

I had some more stuff to say, too, but I forgot what it was. All I can think about right now is the power seat.

[Sea Wolf]

" I got this theory based entirely on observations from trying both a hydrofoil and tabs (although not together). The hydrofoil acts more to lift the stern out of the water and allow the bow to go down. The tabs act more to push the bow down without raising the stern out of the water as much. Can't prove it, nor am I inclined to debate it with anyone. But it sure seems like it to me. It also seems to me that as little draft as the CD22 has, it would be a good idea to keep most of it in the water at the stern."

Mike- I think you're spot-on about the difference between hydrofoil and trim tab operation.

The hydrofoil works only partially by lift, like an airplane wing. This aerodynamic like lift is most all of the upward assisting force when the foil is trimmed parallel to and in line with the hull. The actual amount of total lift from this hydrodynamic force is relatively small compared to the other forces discussed below.

When the motor is trimmed down in the rear, two additional forces come in to play.

First, the forward motion of the boat makes the angled plate move forward through the water, producing a "kite effect"* upward force to raise the stern. Secondly, the motor's thrust in this trim is partially directed upward producing additional force which also lightens the stern of the boat. My guess is this second set of forces are much more powerful than the true lift ever generated. Many hydrofoils don't even have an aerodynamic (wing-like) shape in cross-section, but instead are flat plates, but work well nonetheless.

This would also explain why hydrofoils seem for the most part to lift the stern while leaving the bow less affected, as compared to trim tabs which use the kite effect solely to leverage the bow down. The big difference between the two really, then, is the thrust of the motor, with lift of the hydrofoil having some additional effect on it's performance.

Additionally, the longer, narrower, hydrofoils would seem to work more on kite effect and have less true lift (from the way they are designed), and have a longer lever arm and are thus more efficient at turning kite effect into upward force which would replace the lesser true lift in these designs.

One other thing I think we've noticed is a tendency for the wider, wing-like appearing hydrofoils to "dig in" on tight turns and provide some steering input of their own. Steve (Seabran) mentioned this to me at Shasta Lake, and I've experienced it myself and read about it here and there. I think the extended "wing tips" dig in in turns as the boat rolls and yaws and provide additional steering input from the forces generated, causing the different response and feedback to the helm in tight turns.

I've read quite a bit about the Lencos, and while they're generally favored because of their simplicity of installation due to the simple electric only connections required, they seem to have two common faults. The first is that they sometimes fail from water intrusion- much more commonly than hydraulic units. The second, and more fundamentally flawed criticism is that their range of adjustment is too short to make full use of the tabs and to retract them completely. Some have said it's like buying a set of trim tabs and getting 2/3 rds of a set.

Again, everything is a compromise of a lot of complex interrelationships and choices and whatever works for a given skipper/boat/application is all that counts.

Hope this makes sense! Joe.



* The"kite effect" is named after the common traditional kite in which the forces generated to keep the kite in the air are generated from the upward thrust of the moving air striking the inclined face of the kite, pushing it upward. This is differentiated from aerodynamic lift, which is generated from differential pressures as air flows over a parabolic surface such as the shape of an airplane wing (in x-section).

[Chuck S]

I've never seen trim tabs on a 16 Cruiser, although I'm still considering them mainly to correct lateral trim on the lil boat.

The 16 Cruiser has a very aft Center of Gravity and needs a lot of bow down trim, expecially with more than two aboard and full tanks. Yeah, she's a 2 seat boat, but we bring a folding deck chair which literally fills the little cockpit behind the cabin.

I ran the Honda-packaged SST Hyrdofoil during Amelia Anne's first season. Gave much better trim control than just moving the motor's angle. Even at slow speeds the SST's airfoil shape created a lot of stern lift. But she always felt funny in turns and the boat would sometimes assume a heel to one side or the other I couldn't explain. Quick opposite steering, then center the wheel would break out of this heel.

Since we're totally new to motor boats (other than auxillary powered sailboats for decades) I didn't know if this behavior was normal or not.

Early this season I fitted the PermaTrim plate to the Honda 50. This is a substantial plate which can be used as a step if needed (motor off, of course!). The boat is as responsive to trim as the SST, maybe more; doesn't feel funny in turns; and the strange heel hasn't occurred. Since I also put a 4 blade wheel on at the same time I couldn't judge WOT speed on flat water but it seems about the same.

As good as or a replacement for trim tabs? Certainly on this 16 Cruiser she's doing a good job.

-- Chuck