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Trolling Motor for Dinghy

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eric.werkowitz
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USA
283 Posts

Initially Posted - 06/18/2004 : 17:37:52

Is anyone out there using an electric trolling motor for a dinghy? My D4 needs a motor and I'm considering going electric.

How much thrust do you recommend and what brands?

Any other advice?

Thanks.

Eric Werkowitz
C25 #4969

Edited by - on

Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 06/18/2004 : 19:00:54

Eric,

I tried a 35# Minkota on my D4, and the few times I used it, it seemed to be plenty of power for all but the worst conditions. I built mine with the middle seat as a weather tight lockable storage compartment large enough for a group-27 battery. The only significant disadvantage I've noticed is wrestling the battery in and out for charging and storage. Two smaller batteries, one on each side of the daggerboard (or centerboard) might be a more practical idea. Another thought, depending on your pattern of use, would be to use solar power to charge the batteries in place.

-- Leon Sisson

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Dave Laux
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318 Posts

Response Posted - 06/18/2004 : 19:07:59

How are you going to charge the battery? In my experience it needs it regularly. As a Rule of thumb 1 gallon of gas is 15 horsepower hours. One Grp 24 battery is 1 horsepower hour. A trolling motor and a 2 horse Nissan Yamaha etc. are about the same weight. But a trolling motor and 7 hours worth of batteries is 500 lbs and a 2 horse motor and a gallon of gas is 50 lbs. Some day people will look back at the twentieth century and the way we have wasted the most compact energy source ever thought of and say, What were they thinking of. Dave

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 06/19/2004 : 12:32:04

Thanks for the math, Dave. In my previous response I didn't mention gas because I took the question to be about electric. I agree that a tiny gas motor is a more practcal solution for longer distances, and that the use of an electric motor requires a well thought out plan for battery charging. Obviously much depends on the anticipated pattern of use.

Of the miles I've traveled in my D4, most have probably been under oar power, with sail power a close second. I only used the trolling motor for a few miles when battery charging was readily available.

As for gas alternatives, a 2HP Honda looks mighty attractive, although rather dear for my budget. I would also like to see someone try to market a less expensive tiny 4-stroke, maybe a 4-stroke weed whacker motor and centrifugal clutch atop a forward-only stainless steel reinforced plastic leg with a trolling motor style transom clamp. (Yes, I remember the Cruise N Carry's mixed reputation.) If a weed whacker sells for $200, and an electric trolling motor sells for $200, why does a 2HP Honda outboard cost $700?

-- Leon Sisson

Edited by - on

eric.werkowitz
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USA
283 Posts

Response Posted - 06/19/2004 : 15:39:08

Leon,

Thanks again for the info. I sail out of a slip behind my condo so charging is not a problem for day sailing. I mainly want the dinghy so I can anchor my fin-keel and get to shore without being in water up to my neck.

I also built the sailing option D4. Did you go with the diagonal sprit sail? One of my neighbors suggested that the horiziontal sprit sails better, especially down wind since it is self vanging. But, to get the same sail area it takes a much longer mask and has a much higher center of effort. I'm going with the short sprit, but am considering add a boom for the foot. Any thoughts?

Edited by - on

Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 06/19/2004 : 16:47:07

Eric,

On my D4 I went with a home brew balanced lug rig. That's sort of like a gaff rig, except the boom and yard extend maybe a foot forward of the mast. There's only one halyard, attached that same distance back from the forward end of the yard. There's a downhaul on the boom at the mast, and a loose loop of line to keep the boom from wandering too far from the mast. The advantages of a balanced lug rig include: low center of effort, very tunable with respect to center of effort, twist, etc., reefable, can be raised & lowered with the mast stepped, self-vanging, very light sheet tension, easy to make. Disadvantages would include slight sacrifice in windward performance, but I can't say for sure how much exactly.

In modifying the D4 design, I made so many changes that hamper windward performance, that it would be hard to assign a degree of signifigance to each individually.

For a sail, I cut down a used up triangular main off some other dinghy design. The result has less than optimum shape. For a mast, I used one from a windsurfer which I added a joint in the middle of, like a 2-pc fishing rod. It's real bendy, which probably doesn't improve sail shape either.

Since I don't like daggerboards, and wanted room in the middle seat for a group-27 battery, I designed and built leeboards. In principle, I still think they're a good idea. However, my leeboard mounts extend down to the chine, and so at least one drags in the water whenever the boat is occupied.

I also added large dual skegs with lawnmower wheels to aid in moving the boat around on shore. They work fine for that purpose, but probably produce considerable drag in the water.

Here's a pic of my unfinished D4 when I was just starting to figure out the sail plan. It looks a bit unrefined at this stage, but it shows the general construction features.

-- Leon Sisson

edited to improve spelling

Edited by - Leon Sisson on 06/20/2004 06:23:09

Dave Laux
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318 Posts

Response Posted - 06/19/2004 : 19:51:03

The problem with small four stroke outboards is two fold. First is more parts and more critical parts, valves, valve seats, cam , crank gear, timing belt or chain, oil pump, oil sump, etc. Second is the fact that a two cycle engine produces smoother power, ie. more power strokes / revolution, and thus requires less gear engagement to transmit equivelent tourque. Engineering is a pain and you can tell when it has not been done. Things don't work. Dave

Edited by - on

lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Response Posted - 06/21/2004 : 01:14:57

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Leon Sisson
 If a weed whacker sells for $200, and an electric trolling motor sells for $200, why does a 2HP Honda outboard cost $700?

-- Leon Sisson
<hr height="1" noshade id="quote"></blockquote id="quote">

IMHO, the outrageously high retail price of boats and outboard motors is probably due mostly to legal, not manufacturing, costs. Every time some idiot (often drunk

) gets hurt or drowned in a boating accident

, the manufacturer of the outboard motor can count on being named a co-defendant in the inevitable wrongfull death or defective-product liability lawsuit, as if the negligence or stupidity of the operator is somehow the fault of the manufacturer

. The typical 8 to 10 hp outboards we have on our trailerable sailboats, that retail for as much as $2500 (Yamaha 9.9 High Thrust), only cost a couple of hundred dollars to manufacture, if even that much. After all, there is no rocket science in these small motors - they are not even fuel-injected! - and the basic engine and drive components have hardly changed in 50 years, so all the R&D and tooling costs have long since been paid off. Look at the bigger outboards, the 200 to 250 hp ones that you typically see on competition bass boats - a pair of these on the back of your weekend toy costs almost as much as a new small car, a Honda Civic or Toyota Corolla lets's say (and for crying out loud), and that's only for the motor(s)

! You still have to buy the rest of the boat to bolt the motor too! The apparent "inflation" in the price of a 10hp outboard in the last 30 years is a lot higher than the overall rise of the U.S. Consumer Price Index over the same time period. (If iny of you reading this are Tort lawyers

, nothing personal....

)

Edited by - on

Dave Laux
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318 Posts

Response Posted - 06/21/2004 : 07:14:33

Larry you may be at least part right but the relatively low production rates for these engines is certainly part of the mix as well. BTW a (one) 250 HP outboard costs as much as a car not two. Dave

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