BYYB Forums

Okay Commodores, Captains and crew, here’s my first modification idea and questions.  (Sorry, crew don’t get to be capitalized.  Hey, I don’t make the rules.  I just follow them when I feel like it.)

Like a lot of people, I don’t particularly like the idea of having a motor hanging off the back of the boat.  However, I do very much believe in the importance of having a reliable back-up to my non-existent sailing skills for situations such as entering and exiting the boat ramp area and the inevitable emergency.  Thus, a motor will be included in some fashion.

I am thinking of trying to emulate how Chris Gerkin and “The Barnacle” have a trolling motor placed more-or-less within their respective keels.  It is invisible in the water, provides thrust directly along the centerline and doesn’t bite you in the, uh, rudder.

I think I can mount a trolling motor directly in the centerline of the keel, after deepening the keel sufficiently to encapsulate the motor, and run the wiring up to the hole in the transom for the rudder.  This would avoid having to cut and seal a hole in the bottom of the boat.  I would also extend the depth of the rudderbox to mate with the bottom of the deeper keel.

Obviously this would negate any steering with the motor itself.  But, it would also save me from trying to engineer a steering mechanism conjoined to the current steering assembly.

I don’t think a non-steering motor would create any major detrimental effects.  I believe it would merely trade off maximum efficiency for increased simplicity.

However, my thought of how to reduce that very inefficiency could have pretty negative consequences beyond my experience in a hydrodynamic sense.  I was thinking of trying to increase the effectiveness of the water flow across the rudder assembly from the motor by adding a leading edge to the rudderbox extending under the boat to just in front of the motor. The leading edge would, of course, need to be faired to smooth the flow and reduce drag.  I think it should also extend gradually and then fade back out from top to bottom, roughly like a bell curve.  The rudder itself I could leave relatively unchanged.

The ‘cut-to-fit’ length should catch the flow from across the entire diameter of the propeller when the rudder is turned at about 30 degrees.  For example, when turning to port, the forward leading edge would extend starboard across the flow from the propeller.  The harder the turn, the more impulse could be captured by the leading edge.  Without this addition, half of the propeller’s effort would always be directed aft in a turn.

My concern is, I don’t believe I am so creative as to be the first person to conceive of such an idea.  There really is very little that is truly new under the sun.  So why haven’t I seen something like this before?  Is it that I am just data starved or has this been found to be a really stupid idea.

I think there is the potential to produce flutter in the steering when at amidships or even force the rudder hard over if the flow isn’t balanced in a turn.  Obviously, the consequences range from annoyingly high maintenance to just plain dangerous.  I think that if the center of gravity on the rudder is aft of the hinged point everything should take care of itself, but somehow, I hear God giggling.

My assumptions are that I shouldn’t ‘over engineer’ a damn thing and just stick with the plans.  And attach the troller to the rudderbox like PAR says.  But where’s the fun in that?

Your thoughts?

My first thoughts are get a good set of oars, but most people here now know I detest motors   Your idea isn't new and I have seen it done on other designs over the years, can't remember which ones, sorry.  I have also seen it used with just the prop part of the electric fastened directly to the rudder blade.  It will all work to some degree or other and have it's own drag issues.  Do it and have fun.

Talk to Paul Riccelli (??-sorry if I spelt your name wrong Paul) as I believe it was he & Jim that worked out the details to install it in the Keel of Jim's boat.

Good luck!

On the topic of over engineering, I have a stinkpot on the port side of my transom and have it locked in the straight ahead position.  Once the rudder has some water running over it I can manouver just fine.  It doesn't matter if you have the prop thrusting water over the rudder, although it works just as well.  So in essence, if you have it installed in the keel on the centerline of the boat, you will be able to manouver your boat just fine.  If you hang it over the side and use your rudder to stear the boat, it will work just fine.  Extending the rudder box is just creating more work.

Trolling motors attached to keels have been done, but on a boat this size, it's not worth the drag it generates. You'll lose anywhere from a 1/2 to a full knot of sailing speed with a fixed, even if well faired motor on the deadwood.

Adding to the leading edge of the rudder in the form of balance or with a mini skeg, should be done after you carefully work out the related issues. Common problems would be placing too much balance on the blade, placing balance behind the deadwood (a real no-no, it acts like a brake), wild steering under power (generally you don't want much rudder behind a prop, especially if balanced), etc. The list can be extensive. It's wise to not use balance if a prop is before the blade. It's a lot of math to keep it from steering wild under power.

If you add to the deadwood aft, you'll be adding lateral area to the lateral plane surface. This will "ease" the helm, but could ease it too much, creating a lee helm, which isn't desirable.

Electric trolling motors have two basic advantages; they're reasonably light and they're reasonably small, particularly compared to a small outboard.

I have a mount that I've used on transom hung rudders for several years. I even patented it. It places the motor behind the blade, but in direct contact with it. It's physically attached to the rudder head, but can be easily retracted or removed for normal sailing. It turns with the rudder, for unmatched powered steering and it's compact and it can be raised or removed easily when you don't want or need it out there. This setup also doesn't require sealing holes in the hull or any other special "fabrication".

Sailing with a prop dragging in the water can actually be felt on a boat as small as a Weekender. You'll feel vibration and hear cavitation noise.

Attached is a sketch of how it works. A small easily made bracket holds the motor and tube to the rudder head. I usually bend the tube with an electrical conduit hickie, so it's tight to the rudder head. The bracket has a pivot bolt and two holes, one for the down position and one for up. The sketch shows a pivot bolt which has been changed to a quick release pin, just like the other holes. This permits the motor to be removed, just by pulling the pin (captured ball type pin). The powerhead is removed (easy) and the two motor wires extended to a bulkhead connector, mounted on the boat or tiller. The power head is attached to the tiller, so you can operate it, steer and do everything the tiller normally does. It's usually left in place, but could also be removable.

In the down position, the motor steers with the tiller, providing instant response to helm input (no waiting to have way on to turn). The turbulence caused by the prop is behind the blade, so the boat steers normally if the motor is left down. With a prop before the rudder, 1/4 to 1/3 of the rudder will be operating in turbulent water flow, decreasing performance and steering "bite".

Electric has range limitations and can lack real muscle to punch through rough conditions. It takes about 75 pounds of thrust to equal an outboard's single HP. The prop on these motors is also designed to move a boat at about 3 MPH (trolling speed, interestingly enough), but a few manufactures are making props to fit common brands to increase power and speed. I was even making them for a while there.

In the end, if you have a lot of motoring to do, you'll want a small outboard, but if you just need to clear a dock or anchorage, drag your becalmed butt back to the ramp, or short tack up a canal, then the trolling motor is for you. My sailing permits a trolling motor. Besides, I love to not use it at all and sail up to everything, taking great pride at backing up a boat under sail, to bystanders disbelieve.

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See, this is exactly why this forum is so good.  It helps us newbies find out how and why some of our ideas may not be all that great in spite of good intentions.

Ryerson - I’m getting too fat for using oars on a regular basis  (although a regular basis might help cure that….hmm) but rest assured, I’ll have some aboard for the day when the troller dies.

Shawne - Thanks for reminding me that it’s about getting in the water.  I’ll have plenty of work with out adding any needlessly.

And Paul - Go tell your wife you’re the man!  That looks like a wonderfully simple, but effective setup that would get me the results I’m hoping for.  For most of the lakes in Oklahoma, a trolling motor should be all the power I would need.

Ya’ll be good!

Hey Morgan

I know how you feel about a motor hanging of the back of the boat, but I reluctantly put a trolling motor on my weekender last year.

But having experienced a situation with high wind with my only priority was to get back to shore ASAP the trolling motor did not measure up.

I just got a 2hp gas power outboard and give me a warm and fuzzy for the next sail.

Building a boat is great but the only bad thing about it for me was that I spent way too much time over thinking it. After all, the goal is to get in the water.

Just my 2 cents

Morgan, I tell her (the one that must be obeyed) all the time, but I just get a swat in the back of the head and something added to the list. You'd think I'd have learned by now . . .

Morgan,  I have a small (very small)  2 hp outboard, that I always take along in my Whitehall.  We use it to get back to the dock or back up stream in the river so we don't have to row all the time.

I normally carry it in the bottom of the boat,  when I build my Vacationer, in envision storing it in the compartment in the stern of the boat that the steering mechanism goes through.  It that is not big enough, then I will store it under the seats in the open part.

It works well to move my wife and I and a 20" Whitehall along up stream on the river.

I built the boat to row, but after a mile or so,  it gets to be fun no longer.

I'm planning on a Super Skipjack. (Possibly several)

1. R/C model boats use a flexible shaft in plastic tube, sealed, from the prime-mover in the bottom of the hull to the screw at the aft end of the keel. Preferably water tight.

2. R/C model motor-gliders use a folding prop.

Now, I'm not sure yet just exactly what size trolling motor I'll be using. One not too big for the SSkip, I expect. I plan on assembling the keelson with a slot in the center keelson laminate and install a suitable flexible shaft, along with seals, collets, and a thrust bearing, etc. I don't know if there is such a thing as a folding prop for said trolling motor, and if not I just might develop one. If the hub of the required prop is larger than the width of the keel, I'll add fairing blisters to the aft end of the keel.

Needless to say that reverse thrust won't be available. And, folding props tend to be engineering marvels. But, adding a bit to the complexity of the ship while she's on the ways, I figure, tends to be better than additional operational complexity. I want to be able to tell the motor to go and it will, without adding too much drag while it's not. Also, the weight of the motor and batteries will be more amidships rather than all the way aft. The trick, of course, is to keep the water out, but it's only a few inches of water....

Just a thought or two.

Dale

Paul Riccelli said that "Sailing with a prop dragging in the water can actually be felt on a boat as small as a Weekender. You'll feel vibration and hear cavitation noise."

I have to concur, and not only on boats that small. I once chartered a Janmor 25 (a Polish-built 25' soapdish, er... fiberglass boat with ca. 400 sqft of sail and a modern foil centerboard) and the motor mount parallelogram didn't retract all the way up.

Cavitation - check
Vibration - double check
Slow as hell - yep!