Gardner Surf Dory Outboard Well

[Gardner Dory Enthusiast]

Hello to all.

I have a John Gardner 19' Surf Dory to which I plan to add an outboard well. I wonder if anyone might be able to advise me on the following points. Maximum horsepower for this application (I am leaning towards a 8hp 4-stroke Yamaha, 83lbs.) Long shaft or short shaft motor/height of outboard well. Depth of prop below dory bottom. Is steering viable using the outboard only, or will I require a rudder? Any other thoughts about well design would be much appreciated.

Many thanks for any input.

[Tar Devil]

Welcome to the forum, GDE.

I can't offer advice... there's several who have experience with engine wells and I'm sure they'll be along shortly.

That's a sweet boat. Got any pictures?

[SaltyD from BC]

Welcome GDE, very nice boat you've got there indeed.

Just had a look at my dog eared copy of John Gardner's 'the Dory Book' there's an illustration on pg 123 showing a well designed for a Banker which would likely do fine on your boat. There's no dimensions though..

Somewhere else in the book he highly recommends a stationary outboard and steering with a tiller. Much better tracking and stability he says which makes a lot of sence. This is the way I'd go and I'd look into a cover for the engine box to keep the noise down.

For proper elevation of the motor relative to the dory's bottom, as with any boat you want the cavitation plate at to about 1/2" below the lowest point. I think the proportions would look best with a short shaft engine (15" leg) to keep the motor down low and not sticking out like a sore thumb. Especially if you choose to put a lid over it. Long shafts are 20" so the engine would be up that much higher. I'd go down to a place that sells engines and get some measurements of both short and long shafts from mounting bracket up to the top of motor, and from mb to the cav plate (which should be right close to 15 and 20 inches respectively). Then go to your boat and see which makes sence for you.

Good luck with it.

[Tar Devil]

This is the way I'd go and I'd look into a cover for the engine box to keep the noise down.


If you do this, make sure it's ventilated. IIRC, Harry Bryan has done some articles in WB on the subject.

[L.W. Baxter]

I built and have used for several years a 17' Dion Swampscott with a motor well.

The 19' surf dory is somewhat larger but I think not enough to change the motoring requirements. I use a short shaft 5 h.p. Nissan 4-stroke, which weighs about 55 lbs. If I were powering a surf dory I would use something very similar. If anything, 5 hp is too much for the hull; 8 hp would be useless, in my opinion. No sense in the added expense and weight. What might be even handier would a be a little 3.5 horse with integral gas tank, depending on how you plan to use it. If it will be a dedicated motor boat, 4 to 6 hp with an external tank would be best.

Here is a picture of my dory under power. This is probably at about half throttle, maybe less, and it is already certainly at "hull speed". At full throttle, the transom is fully buried and water will start to boil in through the sculling notch! I can forstall this by putting more weight forward, but she only goes so fast before she wants to bury herself.

http://farm3.static.flickr.com/2057/2531465313_ca183c2645_b.jpg

No need for a rudder.

Make your well about 15" deep for a short shaft motor. I wouldn't use a long shaft, it is not neccessary and will be more cumbersome.

Make the well and the hole through the bottom of the boat as small as possible for the motor you intend to use (best to buy the motor first and make the well a custom fit).

You can put a rubber boot over the bottom of the hole to minimize surging of water up into the well.

Build the box at a rake of about 10 degrees relative to the bottom in order to have a full range of trimming options for the outboard (outboards are not optimized for a perfectly vertical transom).

--Lee

[neilm]

How fast is that Dion Dory pictured above going?

[L.W. Baxter]

Neil, I doubt it will do much more than 5 knots before it plows it's way underwater. The same is going to be true of the surf dory, give or take a knot. Obviously, against a moderate river current it is slow going. Against a stiff current it's no-going.

In the picture above, my boat is probably doing about 4 knots, according to GPS (grandpa positioning sensors). That's my parents and my son aboard.

[TerryLL]

Greetings,

Years back I built a 23-foot Cape Ann dory and used a 10hp 4-stroke Honda in the well. This is a larger and heavier boat than the Gardner surf dory, and the Honda 10 was more than adequate. The 5hp would probably do nicely for your boat, but I would recommend the 8hp. There will be times when you are loaded down, beating into the wind and waves that you will appreciate the reserve power, and you will get longer life out of an engine that you can operate at less than full throttle most of the time. I used the long shaft motor because of the draft of the Cape Ann, and even then occasionally took water over the well top when heavily loaded in bad weather. The short shaft will probably work fine for your shallower hull. I steered exclusively with the rudder but often wished for the maneuverability of motor steering, especially when docking.

The best, TerryLL

[L.W. Baxter]

What Terry says about the 8 hp may be true.

One more thing I will add, though. The 8 hp will weigh close to 80 lbs, while the smaller motors will come in under 60 lbs. This weight difference won't matter much to the boat, but it will matter to the guy who is lifting the motor into and out of the motor well. I know from experience, even with the 5 hp, I sometimes strain my gizzard setting or removing the motor while standing beside the boat. It's a matter of leverage. And if you want to set or pull the motor in the water, it becomes a matter of balance. Unless you will leave the motor in place more or less permanently, that should be considered.

[Thorne]

Truer words were never typed. Particularly with a well, you'll be heaving, hoisting, and lifting that motor all the time -- so the lighter and smaller the better.

After all, if you'd wanted a speedboat you'd have built one, right?

;0 )

[kenjamin]

A yamaha 4HP weighs 47 lbs., has all the power you need and then some and is one of the smallest motors with a remote tank. I push my 20' double ender Caledonia Yawl at hull speed at half throttle and it sounds like it could run forever at that speed. With a six gallon tank, it will seem like forever. I use a three gallon tank and that seems to be plenty for a day's fishing.

http://ford.physics.fsu.edu/Birdrack.jpg

http://ford.physics.fsu.edu/XenaDrive0430.jpg

The driveway picture was taken before the installation of a beefy oak removable motor mount that allows for storage of the motor laid flat in the well. There's an o-ring seal on the port that keeps the stored motor dry. The port's bottom is exactly in line with the bottom of the boat for efficient sailing or rowing with the port in place and the motor stored. My port is clear 1/2" Lexan (scrap from a dance floor installation). It's really neat to see the bottom going by when in thin water and sailing or rowing.

My motor is a short shaft which allows for thin water cruising. I especially like standing and steering with the rudder. There is no vibration in the steering so it is very comfortable and you have one hand free to wave to curious passersby like you would on a proper motor launch. Don't forget to rig a remote kill switch if you go the midship motor route. The motor can be lifted by one but being in the middle of the boat, it is very easy to do with two.

[cedarribs]

To further complicate the question, I assume the wells described don't allow for tilting the motor up for shallow water, trailering , etc. Is it possible to design one that allows for the tilt, or would it become the "tunnel" type like in a semi dory?

[kenjamin]

Theoretically speaking, it would be possible with enough Lexan and a large enough o-ring seal to create a big enough round cornered rectangular port in the bottom of a double ender like the Caledonia Yawl or Gardner's Surf Dory to enable a hole large enough to swing up and completely retract the motor but it wouldn't be cheap. I was lucky in that I got enough 1/2" Lexan to do my 10&1/2" port for $60 when it was $120 worth but it was left over scrap from a dance floor so I got a deal. I could have used plywood but the clear port is very tough and fun to look through. The o-ring seals were $26 each but I had to buy two to get the minimum order amount. I was also lucky to have a friend who is an instrument maker to do the machine work (I still owe him two more sailing trips). The Lexan flange glued and screwed to Xena's bottom (that the port mounts to with four wing nuts) could take a pretty good hit from the motor's lower unit and not be affected much. If it did fail, it would not flood the boat – just the motor well (which of course is already flooded when using the motor). When using the motor in thin water, I stand to get a better look at the bottom and avoid running the prop on the bottom. My propellor still looks new – no paint missing yet.

[Frank E. Price]

It would add a lot of complication, but theoretically it should be possibe to design a sliding OB bracket that would allow you to lift the motor straight up far enough to clear the bottom. If it was used only for beaching the change in center of gravity shouldn't be a problem, especially with a very small motor. Would take some noodling, but I would think it would be better than making the hole in the bottom bigger. Just a thought.

Frank

[Thorne]

At some stage you will reach the point where it will be easier and safer to mount a small outboard on the side of the boat, rather than cut ever-larger holes in the bottom and mount sliding brackets into the well. It also puts that noisy, smelly thing a bit further away from captain and crew...

Here's the current Gold Standard of the small outboard world mounted on Bill Doll's faering on the Petaluma River last year -

http://www.luckhardt.com/petaluma-3-07/petaluma-3-07-Images/18.jpg

[Frank E. Price]

Looks very nice, but . . .

Frank