Small sailboat Design - advice requested

[PAR]

A datto blade in the table saw does quick work of the bird's beak. Two 45 degree passes on the table saw will also get the job done with a regular blade. Use good feathers, as the stock is light and will "buzz" pretty good. Spend some time with your setup so you can cut an "asymmetrical" stave. It's a lot easy to smooth this style of birdsmouth and since the stick starts out as an octagon, the lower portion of a mast can stay that way, which looks nice and is often seen of larger bow sprits. The asymmetrical layout is also slightly stronger.

[ancient kayaker]

Originally Posted by bistros

...very simple routing jig to cut the birdsmouth ,,, I'm going to make my mast straight for the first two feet and then tapered down from there.
--
Bill

... neat idea for the jig. I just found a 90 degree vee bit I didn’t know I had! That should simplify things considerably. I am making this mast straight but a tapered mast doesn’t look too difficult if I can only start with a straight plank.

Originally Posted by PAR

A datto blade in the table saw does quick work of the bird's beak. Two 45 degree passes on the table saw will also get the job done with a regular blade ... the stick starts out as an octagon, the lower portion of a mast can stay that way, which looks nice ...

I don't have a table saw but I can use my cute little Bosche palm router with a vee bit to cut the vee before cutting the stave off the side of the plank, less handling than cutting plain staves and cutting the vees afterwards. As I am half-way through the plain beveled staves I will go with that for the lower 2.5" dia section, and try the birdsmouth method on the upper section; I think it will be quicker and easier.

I think an octagonal mast will look cool, with the corners rounded slightly for comfortable handling. Full rounding would weaken it right at the joints.

[PAR]

I spec mast sections for birdsmouth at the joints, which are the narrowest portions of the stave wall. So, yes, you'd have a slightly stiffer mast if the corners were just eased. It would also be slightly heavier too.

Have you had a chance to weigh Dace yet?

[ancient kayaker]

The completed hull, ready for finishing, is 58 lb (26 kg), so she should be right on the target weight of 60 lb when painted and varnished.

[ancient kayaker]

I have put mast making on pause for a few days while I finish the hull, as I want to get her in the water as a row boat first. I want to try a few experiments in the pool to test stability and establish procedure for righting after a knockdown, re-entry from the water and suchlike - the sort of stuff I like to know about a new boat before I take it into open water. I prefer to do this before the water gets too cold!

Also I ran into problems with the wood winding all over the place after the staves were cut. Although all came out of the same plank, some stayed straight while some curved and others twisted; not usable. Disappointing as only one stave has a knot that requires a scarf; it seemed like a clean piece of spruce. I may use clear pine instead, and increase the wall thickness.

[PAR]

Yep, it's impossible to see all the internal stresses inside a piece of lumber, until you release those with a saw and allow it to take a more natural set.

[nukisen]

hey "Ancient" !
I can see your job has given result. I cant stand it without knowledge about how it will appear in the water.
Hahaha I just love the idea about the Wheel to make it easy to handle the boat onshore.

As you can see my projekt has taking a little
jump. But mine will not be as good looking as yours. I also think I have spent a whole lot of less hours. Also I am still a happy amateur. The design I made was meant to be sheap and easy built. Cause I just want to test another way to use the wind.
As I am not earning a lot of money, and also have four boys. The sheap way to build is important for me, and i have spent about 20 us dollars so far.
And it looks like the budget ends with about 40 bucks .

[Raggi_Thor]

Janne, (Nukisen), I hope we don't hijack theis thread now, but I'm a bit concerned. You write on your web page that your little boat will weigh 60kg and have a displacement of 110kg, and approx 40kg of ballast. What about cargo or crew?

[nukisen]

Dear "Raggi"!
Thank you for concerning.
Maybe I have not explained this very good at my site. I have to update this.
About 200 kilos is calculated and approximately 100 kg netto wight.
So The extra 100kilos is myself. And max load will be around 200 kilos. If someone dare to participate on a tour. And of course then the recistance will bee higher. The crosscurve tells me that I still can tilt the boat for 60 degrees.

Also, I have built a little bit further to.

Excuse us "Ancient"!
Hope you dont bother that we hijacked your thread.
I have showed the excelent solution with oars and the wheels, and I can tell that I am not the only one who are impressed. I do like it a lot.

[ancient kayaker]

Not much done lately, been recovering from an injury and preoccupied by family troubles. I was worried about the strength of the boat, so I did some testing. Put her up on blocks and walked all over the unsupported bottom, didn't even creak. Also bounced on the seats looking for soft or weak spots, everything held up under my weight although there is one area that creaks a little. Not where I would normally sit, so I will accept that. Basically she is waiting for finishing once I can get out from under my other problems. She will be tougher after she is finished as I intend to put a row of brass screws into each load-bearing joint as a backup to the glue.

[bistros]

Originally Posted by ancient kayaker

Not much done lately, been recovering from an injury and preoccupied by family troubles. I was worried about the strength of the boat, so I did some testing. Put her up on blocks and walked all over the unsupported bottom, didn't even creak. Also bounced on the seats looking for soft or weak spots, everything held up under my weight although there is one area that creaks a little. Not where I would normally sit, so I will accept that. Basically she is waiting for finishing once I can get out from under my other problems. She will be tougher after she is finished as I intend to put a row of brass screws into each load-bearing joint as a backup to the glue.

Hope everyone recovers and is well. Testing sounds like it was successful.

I'd think about the brass screws - unless you predrill, and sink them into epoxy you may be creating more trouble than you solve. A screw is a water/moisture vector. Sounds like the boat is strong enough as it is.

--
Bill

[dskira]

Originally Posted by ancient kayaker

Not much done lately, been recovering from an injury and preoccupied by family troubles.

Hope everything find.
cheers
Daniel

[ancient kayaker]

Originally Posted by bistros

Hope everyone recovers and is well. Testing sounds like it was successful.

I'd think about the brass screws - unless you predrill, and sink them into epoxy you may be creating more trouble than you solve. A screw is a water/moisture vector. Sounds like the boat is strong enough as it is.

--
Bill

I installed roundheaded steel screws to clamp during gluing; these have now been removed. I plan to countersink before the final coat, then bed the screws in caulk. Mostly the screws are a backup.

I am concerned that, if a linear glue joint starts to fail at one point, it will then "unzip" the rest of the way much the way a crack propagates. The screws should stop that. Probably overbuilding, but that's not a bad thing.

[bistros]

Originally Posted by ancient kayaker

I installed roundheaded steel screws to clamp during gluing; these have now been removed. I plan to countersink before the final coat, then bed the screws in caulk. Mostly the screws are a backup.

I am concerned that, if a linear glue joint starts to fail at one point, it will then "unzip" the rest of the way much the way a crack propagates. The screws should stop that. Probably overbuilding, but that's not a bad thing.

Terry:

I did some ad hoc failure testing on the Titebond III glue prior to using it here on Thomas' boat. I wanted to see how and when it would fail on a chine log / plywood joint after curing. Like you, I'm a little obsessive about materials. Since Thomas' boat has been designed/built for low cost and parental homebuild with building center materials (no Okume, pine stringers) I wanted to see how strong it was going to be.

Once cured, the Titebond III / plywood joint is basically stronger than a comparable screw / yellow carpenter's glue joint by a couple orders of magnitude. Placing extreme sheer on the chine log, attempting to "unzip" the joint resulted in the plywood failing and delaminating well before the glue joint failed. Joint strength is comparable to an epoxy fillet with good colloidal silica content.

All my testing was done assuming a dry, well maintained joint.

I'm more than convinced the screws are not needed. I removed 80% in Thomas' boat, and left in only those providing support to areas where major bends were in the chine logs.

For what its worth.

--
Bill

[ancient kayaker]

Bill:
you are quite correct, Titebond III is far stronger than any of the materials I use and probably any of the common woods. I didn't explain my concern very well.

Let's consider a wood plank with a chine log glued along one edge. Most of the forces exerted on the plank will pass through this joint, and compression and sheer forces can be ignored for our purposes.

Any locally applied force resulting in tension across the joint will, if severe enough, crack the plank at that location leaving a thin layer of wood attached by the glue to the chine log, because wood is weakest in tension and across the grain. Now there is a crack in the joint which results in stress concentration at each end of the crack, and if the force is maintained the joint can "unzip" along a considerable length. It's only the wood splitting, a familiar thing but it is still a failure, even if technically not actually within the joint.

A screw passing through the thickness of the ply into the chine log will transfer tensile forces to the outside surface of the ply where they will become compression, which the wood can handle much better. If the wood on the inside of the joint fails the wood under the screw head starts to crush, absorbing energy. The screw creates a strong point preventing further crack growth.

A siple glued joint is indeed stronger than a simple screwed joint, but the screwed joint does not have a catastrophic failure mode. Using both gives the best of both worlds.

I only use screws in addition to glue in locations where a sudden failure can be disastrous, mainly the underwater joint between the bottom plank and the rest of the boat, where my weight can be concentrated near a portion of the joint resulting in failure onset. It is more of a factor in a lightweight boat such as mine where the ply planks are flexible allowing force to concentrate on a small portion of the joint.

Interestingly I do not use glues in my canoes. That is because the canoe does not permit me to stand and move around, I stay on the seat which is designed to distribute my weight into the boat's structure.