Does a hydrofoil improve performance in small outboard application?

[kfa4303]

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.

Hi Jerry. Have you tried to just clamp your motor a few inches higher up on the stock transom. The underside of the transom bracket on the motor doesn't actually have to rest on the transom itself. As long as the clamping bolts are tightened down sufficiently and the motor is secured with a safety chain, you can easily gain 1"-2" without having to get a jackplate, or tabs. However, if you should find that you still need to raise the motor a little more, you can always make a small transom riser out of aluminum angle and some scrap lumber, both of which are readily available at any lowes/HD for under $20. There lots of DIY versions of transom risers here in the forums if you do a search. Best of fall you can use any leftover aluminum angle to make some fixed "dumb" tabs like in the pic below. They aren't adjustable, but they can still aid in stern lift. Here's a great link.

microskiff.com - Gheenoe Upgrades



Simple bolt-on transom riser:
View attachment 212975

Here's a shot of my motor on my homemade riser:

 

[Jerry_NJ]

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

Great, my first-try plan was to simply clamp the engine on the existing transom higher - using a spacer/shim on the top of the transom for the weight to sit on. Indeed a safety chain, as I worry about any ideas I come up with ending up with the engine doing a swan dive into the deep six. The last picture is very simple and looks very much to the need, should work. Just have to swallow hard while drilling large holes in the transom for the bolts. Are the bolts Stainless Steel?

Thanks too on the Lowes, I know they have metal bars and plate but I didn't ever notice they have "structural" aluminum. I have learned here on this forum that I can't use pressure treated lumber on aluminum. That would have been my first choice for wood used around water.

 

[kfa4303]

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

Hello again Jerry. Yes, you want to use stainless steel hardware. You'll want to dip and pieces that pass through the hull in a bit of 3M 5200 marine caulk as well. Lowes/HD sell everything you need including the aluminum angle, as well as flat stock and square tubing. Most of it's 1/8", but that's enough for such a small motor. You really only need a few lengths about 12"-18" long, some stainless hardware and a chunk of wood. Here are some pics and links that may help.

The Online Fisherman Forums :: Topic: Homemade Jack Plate! (1/1)
www.customgheenoe.com • View topic - Homemade Jack Plate
microskiff.com - Riser plate on a 15-4 Gheenoe (cool all-wood version)
The Online Fisherman Forums :: Topic: How to build your own Jackplate (1/3)
http://forums.iboats.com/boat-resto...lt-high-jack-plate-post-your-pics-241917.html
Jack Plate Installed w/ Pic, REV tested and need some advice - TinBoats.net

 

[64osby]

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

After raising your motor take a look at the tilt. In your pics it looks like you might be able to decrease the tilt. Move it in to the 2nd hole.

 

[Jerry_NJ]

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

I looked at Lowes and didn't find any structural aluminum, just thin stuff and some "L" beams were very small, less than 1" on edge.

Looking more at my boat I noticed there are two holes through the transom, about 5/16" and 12 inches apart, 6" each side of the center line of the transom.

I know the previous owner had a 25 HP on the boat and bet he used a jack mounting. He sold the boat to me with a 9.9 HP Yamaha on it that was just clamped to the factory transom, which isn't working out well.

How about using some steel, say 3/16" steel plate that is isolated from the transom with rubber, or how about heavy duty sacrificial aluminum foil? I'd think a steel plate about 20" wide bolted to the inside of the transom via the two mentioned holes and a couple more holes (4 total) to which a wood could be attached to receiver the motor clamp... isn't the motor clamp steel?

My transom has a 2" drop from the boat bulkheads on either side, so the pictures of putting a wood filler across the drop in the transom top looked interesting. Raising the engine mount by 2" would be about perfect for my boat.

 

[rheagler]

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

It would be a bit of a hike for you, but there is a metal supplier named Fazio's in Glassboro NJ that has all the aluminum you could ever want or need at very good prices.

 

[kfa4303]

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

I'd jump on that. Good scrap aluminum is hard to find. I'm always on the look out for old ladders and shelves by the side of the road.

 

[Jerry_NJ]

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

Thanks, what I want to do is rather simple, just raise the engine a couple of inches, I don't need or want an adjustable transom jack.

Given the opening on the Yamaha engine clamp isn't much wider than my transom means I can't add much to the thickness of the clamp area by sticking something thick up above the existing transom top edge. Whatever I "stick up" has to be strong enough to deal with an engine that weighs about 100 pounds and which exerts is force to move the boat via the transom.

It should be possible to continue to carry the weight of the engine by it pushing down on the top edge of the transom, now higher to raise the engine. When going forward the engine force will continue to push via the wide area of the engine mount that rests against the back side of the transom. When backing the extended mount area will have to deal with the movement force.

Otherwise, I have to build a "box" like structure behind the transom that holds the engine and then transfers forces to the transom via the box mounting to the transom.... much as the big boats do (the 225 hp engines on pro bass boats). This would of course work but is much more than I think is necessary and that I am willing to do. I can always live with the inefficiency of the engine prop being too deep in the water.

EDIT: Ha, the scrap aluminum eye, yes I have looked at a couple of ladders and at my "cutter's edge" which helps one cut (like a sheet of plywood) long straight cuts with a circular say. I have in fact considered taking it as I rarely use it... or to look to see what they now cost, it may be less than what one would pay for aluminum stock for a place like Lowes/HD if they had it. Some of their metal pieces look high priced to me. The cutters edge is thin but has ribs to give it stuffiness and is about 4" wide. I think I could adapt a run of this stuff to meet my needs.

 

[Jerry_NJ]

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

Sorry if I am guilty of multiple posts.... but the information below fits in discussions here as well as one I started my transom question - yes they are related. I posted this information on the transom thread but no one responded. Looking at the history I see this thread is in fact the one that led me to conclude I needed to raise the engine above the factory transom height. Below is what I did, if only temporarily to see if the small rise will help with better engine performance.
discussed transom jack (engine physical positioning) and a hydrofoil addition to the anti-cavitation plan on the engine to make it move more onto a plan when at full power. Boat is a 14' Discovery (Grumman like) and I think it wallows along when at full power.

In the pictures the 4th show a "quick fix" to raise the engine about 3/4" inch. The engine may still be too low but I will give it a try. The 3rd picture shows I have added a 1/2" (exterior) plywood piece 2' by about 8" to help hold the spacer put on the top of the transom, visible in picture 4. The bolts through the transom are 5/16" stainless steel with a washer to spread the force on the backside of the transom (I many need larger washers such as can be seen on the inside, up against the plywood).

The other concern I have is the transom itself. The first and second pictures are typical I think. To my eye it looks like I can gain access to the area between the inside and backside of the aluminum by removing the end caps, picture 1 shows the LH side, same on the RH side, and then remove the aluminum cap, about 1.5" wide, focused on in picture 2.

My plan is to replace the plywood inside this area as it seems to be gone or soft at the top. The boat is rated at 35 hp or less, I use and will use only the 9.9 hp shown.. and I don't use a transom saver when transporting the boat...never have with this size engine. The soft transom is as purchased used, not something I caused.

Welcome any reactions, especially to the plywood addition to act as a 3/4" transom jack extension. Does it look strong enough? I have run the engine at least 4 hours on this boat with the engine clamped to the transom with just a spacer between the two attachment screws and the inside of the transom to spread the load on the transom already described as soft.

 

[SumDumGuy]

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

I run mine like seen in picture 4 (w/o the ply) with the 1x2 "jack" - no issues. AS long as you can get the clamps something to clamp to there should not be an issue (within reason).

If you think the transom wood is gone, rotten or weak, then pull the caps (corner and transom) and replace the wood.

 

[crabby captain john]

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

WoW!! This has really gone on. A foil will be of no help with the current motor/transom match. Unlikely there is enough transom height that simply raising the motor will fix without building up the transom. Adding a 'foil to the current situation would be like buying aspirin to cure cancer.

 

[Jerry_NJ]

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

Yep, as observed, "this has been going on for a long time, in part because I work very slowly, if at all : )

I started with just the spacer on the transom to raise the engine 3/4", the screw clamps were still below the transom cap. But that's where the real softness of the transom is, thin inside aluminum pulls away from the transom cap if it is squeezed too tight. I even put in a piece of wood under the screw clamps, but it didn't look good. I think purchased a piece of exterior plywood, as seen in my pictures. I reused two 5/16" holes in the transom to bolt the plywood to the transom. This also gave me something to transfer pressure from the screw clamps to the transom "cap", wihich is far stronger (gauge) than the sheet material on the transom.

I have today purchased two SS larger washers, 1.5" in diameter, like the ones shown on the plywood side, to better spread the pressure of these two bolts to the outside (back) transom sheet metal. I will now tighten the two bolts a little tigter.

Yes, this ia all about my original post and the "foil".. this is the first step, seeing is a slight raising of the engine produces better engine performance at or near full throttle.

I may then decide that is all I need, I am not going into any speed competition, just want my fishing boat be able to move faster and be more fuel efficient.

 

[crabby captain john]

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

The 1st and most important thing to do is to have the motor where it needs to be. As there is softness in the transom now it will need replaced. Replace the wood with a transom of a height the motor will be hung where it was designed to operate efficiently and safely.

 

[greenbush future]

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

raising your outboard 3/4 of an inch seems like way too little to have any effect on your issue. Based on your pictures, I would have estimated you needed to raise the outboard about 3-4 inches to line up right. With rot in your transom, I don't think you could do this safe to operate long term, but you could raise it by putting a 2x4 as a spacer, then run it and see if that is the correct height. Too high, adjust and run again. You need to know exactly where the best height is, them replace transom for safe boating. And don't drill any holes in your transom until this issue is fixed, that outboard doesn't need through bolts to test and adjust.

 

[AChotrod]

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

My boat is a bit bigger than his and actually exceeded my expectations for speed. My question is when I get on plane the boat keeps going faster the more I trim it up and only slows down once it cavitates. Would a foil help this.

 

[smokeonthewater]

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

nope

 

[Jerry_NJ]

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

Ya gotta love a simple answer - e.g., "nope".

My idea was to try 3/4" to see if there was any improvement, not optimal performance. I bet too it will take a couple of inches.

I didn't drill any new holes in the transom. The previous owner must have. Surely he knew the transom was shot, but I think can be repaired at its current height for a few hours and few bucks. I think the holes were used for a transom jack as the previous owner had a 25 hp on the boat. I suppose the jack added the strength to make up for the soft transom.... don't know.

I'm not very happy with the seller, I think I would tell a prospective buyer the transom needs work. Rather they tried to sell me on the idea that the 9.9 hp Yamaha was as good as new - almost no hours. When they couldn't get any he cooling indicator hole to produce any water. This blew a hole in the "new" engiine, albeit the impeller is easy enough to change that it was a small deficiency. Turns out too, they had no idea how the Yamaha works (a 1990 engine) - it doesn't have side water intakes to the hose ears didn't supply any water when they tried to demonstrate the engine. I does not appear there was any damage from running it "dry" for a few minutes, event he impeller looked and felt like new, engine runs great albeit with enough cavitation to mix paint.

The boat engine will "see" only some testing, it is winter in NJ USA. I don't plan on spending hours on the lake before March, a clearly limit full throttle running for testing.

I appreciate, and when/if I find some good structural aluminum (with stiffener bracing) I'll consider making a "real" transom jack..then too if I decide I like the boat I may buy a commercial transom jack... and stuff the existing transom with new plywood. The sheet aluminum looks great.

Thanks for inputs... I may even go to a foil when I get a near optimal engine height.

 

[AChotrod]

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

Ya gotta love a simple answer - e.g., "nope".

Works for me.

 

[crabby captain john]

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

OP seems to have his mind made up.... Most often it is less effort and cost to do something correctly. I wish him luck

 

[Jerry_NJ]

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

Old thread, but this update provides closure on what I have tried - thanks to all contributors ideas/suggestions/expertise.

I don't see the pictures of my simple/poor-man transom jack I installed to raise the engine about 1", I can post here (too?) if anyone finds the information interesting enough to see benefit in the 3 or 4 pictures I posted elsewhere - I think it was in a tread I started to discuss my problems with the transom.

The bottom line is the 1" raise in my engine mount greatly improved the engine/boat performance. The boat now easily achieves a "rooster tail" at full throttle (quiet lake water, low winds) and maintains same with a little throttle back/down. I also moved one of my batteries which weights about 40 pounds (deep cycle 50 AH) from a location about 2' ahead of the transom to about 8' ahead of the transom, just behind the front fishing deck (14' boat). I think this helped too. But the bow still rides too high under full power, I believe.

While there may still be improvement to make on the "trim", I am very happy with the result so far and think a Hydro Foil isn't necessary. Some have said looking at my pictures that the engine needs to be another 1" or so higher - may be so but I can't try until I improve my transom "jack".. and structural (heavy duty) aluminum is hard to come by. I plan to open the transom and replace the plywood between the rear and inside sheet aluminum. This could provide a better base on which to add a little more engine spacer on top of the transom.

This is my second 14' aluminum boat running a 9.9 HP. The previous boat had a deep cycle batter at the bow for a bow trolling motor weighing at least 30 pounds or so to the bow. When I get around to mounting the trolling motor on my current boat it should also aid in engine performance.