Scaling the Bolger Single-handed Schooner

[Perm Stress]

"http://www.duckworksmagazine.com/04/s/projects/schooner/index.htm"

there looks to be a bulkhead at front end of rudder box in one of the photos too

[Perm Stress]

"http://chopandquench.typepad.com/photos/schoonerpix/frombow2.html"
"http://chopandquench.typepad.com/photos/schoonerpix/from_bow.html"
In those photos there is no extensions of "planks" siding the keel box, however.
But definite answer is in the plans really ....

[PAR]

I built a Bolger single years ago and going from memory, both the rudder box and dagger case had a single, full width bulkhead at one end and a deck beam at the other. On the dagger case the bulkhead was at the forward end, while the rudder box the bulkhead was at the aft end. The rudder box had another bulkhead in the general vicinity, about a foot forward of it. The plans are fairly easy to follow.

[lboatman]

Originally Posted by upchurchmr

Iboatman,

This looks like a really nice adaptation of an old fashioned heavy design. Everything I have seen makes sense. Pity others don't get it. But I am sure you were prepared for the typical average attitudes.

I had a couple of those at work today, just thought I would offer some support. Too bad you can't immediately continue, I want to see the next steps. I had a friend with a Bolger Black Skimmer an I really wanted to see it built as you are doing.

Nice job.

Marc

Thanks for the kind words, Marc. I wish I could continue, too. Especially now that I've documented it all, I'm really in the mood to get it on the water and try it out. But, there's no point in trying to go against Mother Nature. Maybe I can get some of the small bits done while I wait for her to relent with the temps.

As far as the discussion, I'm thinking that this one is mostly a communications issue, rather than ignorance. Just have to work a little harder making the point clear. But it is nice to hear from someone who actually did get it.

Thanks,

Laszlo

[lboatman]

Originally Posted by Perm Stress

well, it is too difficult for to contact Bolger just now.... maybe some decades later....
.

I hope that it is many decades from now before you can talk with Bolger (unless you attend a seance).

Laszlo

[lboatman]

Perm Stress & PAR,

As far as the extensions go, the way I originally read Perm Stress' question, I thought he meant a full length extension all the way to the next bulkhead forward. Those do not exist in Bolger's design. There are, indeed, a pair of extensions on the keel box that extend 7 1/4 inches forward (again, apologies to the metric world but Bolger's plans are not metric).

The rudder box is attached to bulkhead E at its aft end. The keel box is attached to bulkhead C at its aft end. There is no bulkhead attached to the forward end of either box in Bolger's plans. If you look at the plans in the file referenced by Perm Stress, you'll see that the permanent bulkheads are labeled as 15. There's a 15 at the aft end of each box, but not at the forward ends. The lines in the plan view there indicate deck beams. If you look at the picture I posted back at the beginning of this thread, you'll see that my build follows this arrangement, with the proviso that I haven't finished building the boat yet. The extra structure in the Duckworks picture of Tony Groves' prototype is something he came up which is separate from Bolger's original design, maybe a storage area.

As far as the extensions go, there are none for the rudder box in Bolger's design. In my adaptation, I very deliberately left out the ones for the keel box, too. This was because, based on my calculations, they were as unnecessary in my design as rudder box extensions were in Bolger's. It was not because of sloppiness, forgetfulness or ignorance.

I'm not going to run through all the numbers here, but the general principles were:
1. The length of the hold is 6% smaller so the moment arm is shorter
2. The surface area of the bottom is 12% smaller while the thickness is still the same.
3. The distance between the supports for the bottom is 6% smaller
4. The bearing area of the taped joint at the front of the keel box is 83% of the bearing area of the extensions specified by Bolger.
5. The bottom is preloaded because of the rocker.
6. The bottom is attached to the sides with continuous joints with no stress concentrators.
7. The sides are the same thickness as specified by Bolger

Taking all these factors into account, actually solving the plate equation for stiffness and even borrowing a little time on the finite element analysis program at work came up with the result that in my adaptation of Bolger's design the forward extensions on the keel box were unnecessary. The bottom is stiff enough to absorb the forces and resist the stresses without them. This may or may not be the case for any other design in the world, but it seems to be for this one.

This isn't just theoretical, either. A boat I previously built had a very similar structure to this one. It was only 14 instead of 18 feet long and the bottom was only half as thick as the schooner's. I used it for 10 years so I got to see how it flexed and how it stood up to use.. Actually experiencing that amount of flexing and seeing the conditions under which it flexed gives me confidence in the schooner adaptation.

And as I told Marsh Mat, Mother Nature will be the ultimate judge on whether I got this right or wrong. If I do end up having to add the extensions, I'll be posting that information, too.

Laszlo