Friday, June 22, 2012

How to Make a Displacement Hull Plane

The Bartender line of fishing boats has a reputation as a superlative surf boat. The Coast Guard has used them as rescue vessels. As doryman everywhere know, a good surf boat is double-ended and is thus less likely than a square transomed boat to broach on a following wave.

Unfortunately the double-ended hull will not plane under normal, non-surfing conditions, no matter how much power they produce. So, George Calkins designed a spray skirt for his power dories to provide more lift at the stern.

The nineteen foot Bartender in the lean-to out in the boatyard has never been outfitted with a spray skirt, as far as I can tell, but it has one now. Frank, the current owner has been frustrated that this boat tops out at 10 miles-per-hour.

Now, that would be just fine with me. Mentioning this to Frank made him laugh.

If this were my boat, I'd have no more than a ten horsepower motor on her and be happy just puttering around. The hull drives easily and this could be a very economical package.

The boat has a 40 horsepower motor however, and a rated speed of 25 - 30 mph, which is what we are trying to achieve. The bottom had a keel hog from sitting on a poorly designed, dilapidated trailer which probably contributed to it's reduced performance. I've stressed as much of the hog out as I could, reinforced some old, tired keelson framing and re-welded the offending trailer. All in a days work for a shipwright. The spray skirt was a challenge - the hull shape aft has such a radical camber that the face of the skirt is a helix. I laminated Oregon white oak using polyurethane glue and stainless screws. Didn't have to steam bend anything, but very near.

Frank will be camping aboard this boat at the upcoming Sucia Rendezvous so I'll be able to see first hand how all this works out.

Hope you all had a better solstice than I did. You can see what I was doing on the longest day of the year.

The spray skirt meets the chine at the stern, sweeps up past the waterline about half-way, then on to touch the bow in a fair curve.

Need to clean and polish that bronze half-round for a finishing touch.....

I also prepared some salmon for the Rendezvous. John St Clair is known locally as the Salmonator. He is a prolific fish killer. (many people find it confusing that I spend so much time on the water but don't fish. With friends like the Salmonator, why should I?). Recently he gave me a 20 pound salmon that had been in the freezer for awhile. The best thing to do with a fish that's a bit past it's prime is smoke it. I don't have a smoker, so I slow cooked my fish. After marinating it in a brine and sugar mixture for 24 hours, it was spiced with garlic, onion, tariyaki and sesame seeds. It was then cooked at 170 degrees F, for six hours. Dessicated fish is not photogenic, so I will forgo any pictures. Take my word for it. It's delicious!


Glenn said...

JThere is actually no problem with making a double ended hull plane. It's a matter of displacement, horsepower, waterline plane and shape. The planing skis increase waterline plane and modify shape. I'm with Frank on the speed. Open ocean swells on the West Coast travel at about 28 knots. If you can make 30 you can count on being able to ride on the back of a single wave all the way in, and never have the curl overtake you. That was the point of Calkin's design. The Pacific City dories can do the same thing, but the double ended shape is much more fuel efficient when slowed down to trolling speed offshore.

doryman said...

I knew you could fill in the details. It's always a matter of horsepower, isn't it?

I've seen a double-ended boat surf in (under control) with a dead engine. Also seen a flat transom boat broach and roll. I'm very happy to have not been on either of them at the time.

Glenn said...

I'm with you on the double-ended part Mike. If for some reason (engine failure, low fuel) you can't keep up with the seas, a double ender is much better in surf. Although there's this odd Danish sharp sterned, pram bow beachboat from Jutland... Hint, it's like a reversed Coble, though it's the stern, the pointy end is kept into the seas coming and going.

doryman said...

Frank was pretty happy with his new paint job. As he got in his truck to leave, I heard him say "gotta find some water and try her out..."

jp huza said...

so if you want a boat to "plane", you need to add wings?

just had to add a dumb joke. couldn't help myself.

looks like a very cool boat.

---jp of yakima

doryman said...

jp, I suspect you are not the only one to get the pun. I think of them as fins. In fact, there is at least one Bartender of this design with adjustable trim tabs mounted in this location.

jp huza said...

Sorry to have dipped into silliness after what had been a pretty intelligent discussion.
I've seen a few Bartenders around, and can see why the Coast Guard would have found them to be pretty handy in the rough going.

(The silliness runs pretty deep, though. My brother and I used to trade sideways comments all through dinnertime. They slid right past Mom, but Dad caught them and lectured us forcefully about them later.)

Anonymous said...

If this is a Dory built by Calkins, the row Dory's did not have the Planing surface, and were not intended to Plane. They had the inboard motorwell like the Bartenders, but that was only used to get out thru the surf,perhaps this boat originally was a rowing Dory someone tried to make it into the Dory with the cabin then gave up because of the non planing reasons, or just intended to run in displacement mode anyway.. WW

doryman said...

It is indeed a Calkins. I wasn't aware of a rowing version. That would explain a lot. When Frank got this boat it had a small motor well that did not allow the motor to tilt up. He rebuilt the well to accommodate a bigger motor, which didn't help the buoyancy aft. The cuddy cabin doesn't help much either - this is a very heavy boat compared to it's design weight.

Anonymous said...
(this link will probably go away soon as they do on CL). Here is one for sale, you can see no planing chine. Was a double rower.

doryman said...

That looks familiar - I assume the hull shape is the same?

Anonymous said...

I believe the same hull. I find a lot of people add too much weight to these, they are supposed to be light weight, that is what makes the design work better..

Tommy said...

Question as to how Frank attached the skirt to the hull.
Did he attach the first laminate and then each additional as he was forming the skirt?
Or was it fabricated fully, then attached to the hull? If so, how attached to ensure sealing?

doryman said...

Hello Tommy,
It was me, doing the work for Frank. Yes, I attached the first layer of a laminated fin to the hull. It was approximately 1 1/2" x 1 1/2", through-bolted and epoxied to the hull. Each successive layer was thinner and screwed and glued to the previous. On the last few laminations, I backed the screws out, since they would be planed to shape.