Does a hydrofoil improve performance in small outboard application?

[Jerry_NJ]

Re: Does a hydrofoil improve performance in small outboard application?

I seem to have lost a reply, here's a shorter version.

Davis Instruments Doel-Fin Hydrofoil is not in my Amazon Shopping Cart. I haven't pulled the trigger yet.

Does one size fit all? I have a 9.9 HP, the listing says nothing about engine size.

I note, for example, Sting Ray at Bass Pro Shops comes in several sizes.

I too wonder why a manufacturer doesn't add a few pennies to the cost of manufacture to build with a Fin, then kick &%* on the competition.

I notice iBoats automatically saves a thread being typed... how can we access that saved copy, e.g., the current situation where I thought I made a post, but I can't find it.

 

[JimS123]

Re: Does a hydrofoil improve performance in small outboard application?

Does one size fit all? I have a 9.9 HP, the listing says nothing about engine size.
I note, for example, Sting Ray at Bass Pro Shops comes in several sizes.
I too wonder why a manufacturer doesn't add a few pennies to the cost of manufacture to build with a Fin, then kick &%* on the competition.

Doelfins are universal, I have the same size on my 9.9 OB as my 140 I/O. Only the color is different to match the outdrive color.

Not all boats need them, thus its not practical to install them on everything. Where they shine are small fishing boats that are tiller steered and all the weight is aft, or larger boats that are overpowered and stern heavy for that reason. Older wooden boats, for example, have superior buoyancy, and back then were equipped with more reasonable size motors.

OTOH, look at a VP stern drive made a few years ago. The AV plate is much larger than any Merc or OMC. Did they have a better idea?

 

[JimS123]

Re: Does a hydrofoil improve performance in small outboard application?

How many of those in your club are on motors that aren't set up properly, and could have been fixed by raising or lowering the motor an inch, or using the correct prop, or adjusting the trim?

Just an observation....I don't belong to the club.

Really now, how many people actually tune their boat? Worse yet, how many dealers actually know what to do?

You buy a boat, hang on a motor tight on the transom, and go. The average guy isn't a boater, he's just a guy with a boat. People don't get tune-ups in their car, you can't expect them to fine tune a boat....LOL.

The first point is that they DO have their place, and just because you put one on doesn't mean the boat will self-destruct. The second point is that there are literally thousands of these in use, with happy owners, none of which ever heard they were evil on the internet.

 

[ondarvr]

Re: Does a hydrofoil improve performance in small outboard application?

How many of those in your club are on motors that aren't set up properly, and could have been fixed by raising or lowering the motor an inch, or using the correct prop, or adjusting the trim?

With a foil you may be able to raise it 2 inches.


And foil is a bad name used for marketing, a flat plate would to the same thing.

 

[kfa4303]

Re: Does a hydrofoil improve performance in small outboard application?

There are lots of opinions on dole fins. I would simply suggest that if they worked as well as advertised major manufacturers would build them and/or offer them stock on their motors. You'd also see pros using them, which you never see either. Not to mention the fact that they would do little more than collect huge amounts of river grass and sea weed where I live. All that being said, they do seem to help on some small craft which tend to sit low in the stern. I overcame that problem by raising my motor the proper height and using a tiller extender which give me improved performance and more options on how I drive the boat. Best of all, I didn't have to touch the motor in any way.

 

[Jerry_NJ]

Re: Does a hydrofoil improve performance in small outboard application?

Boy, at only a bit over $30 I'd give the Doel a try but drilling four holes in the engine's ant-cavitation plate leaves me uncomfortable with making the test.

I took some pictures, I can post when I get on my desk computer, and they show the subject 9.9 HP Yamaha anti-cavitation plate about 2" below the keel, is that a problem? My reference Grumman/OEM 9.9 HP i see the anti-cavitation plate about even with the bottom of the keel, and that boat would put out a "rooster tail" like wake even before coming up to full throttle.

If I need to raise the Yamaha 2", how? It is mounted on the factory transom and there isn't anything higher unless I come up with some kind of a riser for the transom. It occurs to me I could put a 2x4 (1.5 x 3.5) on edge at the top of the transom and put structural wood on both sides connecting the 2x4 to the transom and raising the engine 3.5". I estimate that would put the anti-cavitation plate just above the transom, the prop would still be below the transom. The Yamaha also has two smaller "fins" above the anti-cavitation plate but they are much smaller.

 

[kfa4303]

Re: Does a hydrofoil improve performance in small outboard application?

Hi Jerry. The anti-vent pate on your motor should be level, or slightly higher than the keel. It sounds like yours is sitting a little low, which definitely hampers performance. I had the same issue and built a little transom riser out of some scrap aluminum and lumber, but there are all sorts of fixed and adjustable aftermarket jackplates available as well. If raising the motor to the correct height doesn't fix the issue, you may want to look into some simple manual trim tabs like in the bottom two pics. Both are very popular down here in FL where folks try to get as skinny (shallow) as possible <6'' and use them to reduce/eliminate stern squat.

 

[Jerry_NJ]

Re: Does a hydrofoil improve performance in small outboard application?

Transom riser, I'll look for something to purchase but I had thought about a couple of ideas just using wood and I worry about the strength issue even with just 9.9 HP.

Seems strange to me that a boat manufacturer would construct a transom that took something other than a standard 15" or 20" outboard. Mine is 20".

I have no idea on where to get or how to work with aluminum. I assume stainless steel hardware can be used in contact with aluminum. Say for bolts and screws.

EDIT: I did some searching on Jackplate and see lots of fancy stuff that is way beyond anything I need..but it seems your term "riser" may be the same as "stationary jackplate". All I'm looking for is slightly better performance on a low power fishing boat. Most of the info seems focused on "setback" in which I have no interest, I simply want to raise the outboard higher up the transom, no setback. I think I could get it an inch higher simply by putting a 1" wood spacer along the top of the transom and thus simply clamping the outboard higher on the transom... I guess all I have to do is keep the clampscrews below the top of the transom. It appears low cost fixed aluminum brackets are offered that simply bolt to the existing transom and provide for putting motor mounting material (two layers of 3/4" plywood?) between them and above the existing transom. I hate the idea of drilling through the transom but all the holes would be above the waterline so one would not have to make them perfectly water proof.

All said, I can "live" with the lower performance now given my the too low engine mount, and I read this basic problem would make the doelfin worthless.

 

[rallyart]

Re: Does a hydrofoil improve performance in small outboard application?

It's pretty simple. Do what you can to set everything right. Balance the load in the hull so it runs level. If you still have trouble getting out of the hole when you power up a foil of some sort will help with that. There primary purpose is to create lift. It's an inexpensive patch to improve that aspect of performance. A foil can do more but you balance benefits with negatives. I have a foil on my 1980 18' I/O. A huge help for $50. I think about putting one on a 4hp inflatable I have although i know the correct fix is to put on a 6hp. That costs more that $50 so I've done neither yet.
It's a cheap fix for a problem. If you want magic it comes in a different package.

 

[Jerry_NJ]

Re: Does a hydrofoil improve performance in small outboard application?

rallyart... seems you still think the hydrofoil might help, I'll keep it on my maybe list.

Here are some pictures of what I am wrestling with. I tried to upload pictures showing the mount with a tape measure, but I couldn't get them to upload even to my picture folder... they were indicated with a red color circle with what I think is a "!" in the center. Do I have too many pics in my folder?

In any case these pictures document my current mount absent any real measurement references.

I need to better understand how to "manage attachments"... can anyone point to the how-to information?

 

[Scott Danforth]

Re: Does a hydrofoil improve performance in small outboard application?

your motor is down WAY too far. raise it up so the anti-cav plate is just above the keel.

 

[Jerry_NJ]

Re: Does a hydrofoil improve performance in small outboard application?

Here's another attempt to show pics of the existing engine mounting to the transom, which is and no surprise as high and only way the engine can be mounted. This makes me think Discovery screwed up on making their 20" transom, it doesn't match the 20" outboard engine properly. I note, and show, the OMC Evinrude on my similar size Grumman with a 15" transom matches perfectly and that boat/engine was my reference when I decided the Discovery wasn't performing properly - thus looking into the foil.

Hum, worked this time.
The first shows the inside of the transom where I have already put a shim board between the transom and the two screw clamps to better distribute the force onto the transom. There the tape measure shows if I added a 1" thick shim board (same width as the tramsom top trim) on top of the transom the two screw clamps will still be below the top of the existing transom. This would raise the engine 1" and the shim would transfer the engine weight to the top edge of the transom and normal.

Looking at pic 2 it appears the outside might be a problem as the engine mounting face doesn't have a full inch of space between the contact face and the transom top trim.

If I do anything along this line I will try to find a strong point in the boat to tie a 200 pound test rope to with the other end tied to the engine, hate it when the engine goes overboard in deep water :mad-new:

The last picture is the Grumman/Evinrude with a 15" transom/engine and the fit is perfect.

 

[dan t.]

Re: Does a hydrofoil improve performance in small outboard application?

Do hydrofoils work ? Sure they do, and with an underpowered set up like yours one will definetly help. Example; my Quicksilver 270 inflateable with a Merc 6 hp 4 stroke zips around just fine with just me in it (200 lb ), add a second person ( my wife, 130 lb) and it will not get on step. We added a Stingray JR hydrofoil, guess what, it gets up on step just fine. Proof enough for me.

 

[Jerry_NJ]

Re: Does a hydrofoil improve performance in small outboard application?

I've looked at pics of the StingRay in a Bass Pro catalog.. lists for $49, so I'd be inclined toward the DoelFin at $30 and from Amazon free shipping... heck, not a lot of money but why not?

I appreciate your experience but first think I should do whatever I can to get my engine mount up a inch or two without spending more on a Transom Jack than a new engine costs. Not that a new engine would fix the problem, it seems either Yamaha (1990 version) made an error in the shaft length of the 20" model or Discovery did in the construction of their 20" transom. Given Yamaha is still in business and Discovery is not may indicate something.

Clearly a hydrofoil is affordable.

For curiosity, I don't have a inflatable (kayak and canoe, yes) I wonder if it too needs to have the engine anti-cavitation plate (that's what Yamaha calls that plane just about the prop) even with the bottom (flat?) of the inflatable..

 

[jestor68]

Re: Does a hydrofoil improve performance in small outboard application?

The transom bracket has provision for bolting the motor on the boat.

Why don't you set it at the proper height, and bolt it on?

 

[jestor68]

Re: Does a hydrofoil improve performance in small outboard application?

Sooooo, why don't all engines come with one from the factory

Using your reasoning, we'd need to have wings in order to fly.

 

[Jerry_NJ]

Re: Does a hydrofoil improve performance in small outboard application?

Seems I was lost in the "woods" or "water" from the beginning... so tell me how I adjust the outboard up/down relative to how it clamps on to the transom. Such an adjustment has completely escaped my eye and my reading of owner manuals (which I do a poor job of at best). Perhaps my pic 2 in post 32 shows where the vertical adjustment is. The 4 hole choices for the angle of the engine relative to the mount does very little in raising the screw.

 

[smokeonthewater]

Re: Does a hydrofoil improve performance in small outboard application?

he was saying that there are holes in the bracket and you can drill the transom n bolt the engine on higher..... Personally, I have no idea if this is true for your motor or not but I'm just clarifying his statement for ya

 

[smokeonthewater]

Re: Does a hydrofoil improve performance in small outboard application?

Panther Static Transom Plate 55-0405 - iboats

 

[smokeonthewater]

Re: Does a hydrofoil improve performance in small outboard application?

T-H Marine Mini Jacker - T-H Marine Supply MJ-1-DP - iboats