Yawl Boat Design Queries

[ShagRock]

I've been reading up on yawl boats and their construction including different style boats of Norway, Shetland Isles, northern Britain and Ireland. In some designs, much emphasis was placed on 'hollowing' of the garboards which was said to help sailing; but I don't quite understand how this works? Some builders would make the garboards more vertical in placement to the keel, also said to improve the sailing versus rowing capacity of the boat.

It appears that many recreational boats of this type today are built without the traditional external keel. Does the centerboard totally replace the function of the traditional keel? Might a heavier 'workboat' still have a need for both a keel and a centerboard?

What advantage or disadvantage is there to having a square stern on a yawl boat compared to the full double-ender? Is it then still a yawl boat? Finally, can a good yawl boat be achieved just as well in carvel as in lapstrake construction, and why or why not?

Lots of questions, I know, but there are more variations to this boat type than I had been previously aware of. Any thoughts and opinions would be helpful and appreciated.

[James McMullen]

"yawl" has meant many different things over the years. If you mean something like the original "Norway Yawl", then yes, double-ended and lapstrake are part of the definition, and nothing else is still a "Yawl". Of course, that's no longer the only meaning for the term these days. As far as your other questions go, there's pro and cons to everything as everything is a compromise.

But here goes from my perspective:
Yes, a properly shaped modern centerboard completely replaces the need for any other salient keel and gives you better windward performance with less wetted surface area. More vertical garboards is a way to add extra salient keel area--unnecessary complication when you have a CB instead.

Square sterns give more bouyancy aft which can help with load carrying for a given length, but may be disadvantageous in balance and seakeeping in truly rough water or when launching or landing through surf. Whaleboats and surf lifeboats are also double ended by no coincidence.

Lapstrake is almost always lighter and better able to handle drying out than carvel for smaller boats, but after a certain point--around say, 20 ft or so, carvel starts to be a decent option as the scantlings for minimum plank thickness required have caught up for a boat of this size. Having done both kinds of construction myself, I'll tell you that I find lapstrake more elegant and more enjoyable from a sheer woodworking perspective than carvel, and I would choose to build almost any boat lapstrake first if I could get the planking stock for it.

My own favorite boat, Rowan, is a modern interpretation based on the Shetland Yole.

[ShagRock]

James, I am most grateful for your generous and knowledgeable response. This is most helpful coming from a builder of your expertise. Your coverage of the scantling aspect relating to carvel v. lapstake in larger boats adds a new factor to appreciate with respect to choice of build method and materials.

The only other queries I have relate to size of plank material and number of strakes. In some areas of the Northern Isles (with few trees), the planks were imported from Norway. When large timbers became scarcer and more costly, they imported planks in 'shorter' lengths to build the same size boats. So two questions:
1) can a 'glued lapstake' be built strongly enough by joining shorter planks and what are disadvantages to this method, eg. will it require internal framing for support?
2) In the event of not having sufficiently wide planks, can any hull of this type be modified to have a larger number of planks, eg. going with 7 strakes on a hull originally designed for four?

[DGentry]

I think I've learned enough from James to give you an answer:
1. Glued lapstrake is really most suitable for plywood planks, not solid lumber. There's a lot of moisture content related movement with lumber planks, and traditional lapstrake construction is more suitable for that.
And, for all intents and purposes, scarphed planks are just as strong as planks that come that length in the first place - providing the scarphs are done well, of course.
2. yes

Good luck!
Dave Gentry
Feel free to add or correct, James . . . .

[Peerie Maa]

Gordon,
A couple of observations based on the evolution of Shetland boats from Norwegian.
James is right about the CB/ Keel sailing issue, but prior to trailers and tow vehicles the boats were beached and hauled out for storage in boat noosts, so a strong keel was imperative for that reason. This would still be true if they had the glues that we now use to allow us to build leak proof CB cases.

Neither Shetland builders nor Norwegian builders are frightened of using short streaks. This was to allow them to get the shape out of the available stock. They relied on the passing streak to support the scarfe. Their standards would now be frowned on.

When the Shetlanders started building their own boats, they increased the number of streaks over those of the imported Norwegian boats because the boards to which they had access were narrower. This gave an added advantage that they could refine the shape more against the disadvantage of more labour and slightly heavier final weight.

[ShagRock]

Nick and Dave..thank you gentlemen for your input. Taken together, all this information leads to a supposition that one really needs to appreciate the purpose for which a boat is built and where and how the craft will be built and put into the water.

I took particular interest in the Shetland boats because of their use in the 'haaf' fishery..a great historical story in itself. To venture miles off the coast for several days at a time in a small open boat is not only a testament to their superb sailing skills but also to the high level of trust they placed in the the superior nature of their boat's design.

There were so many unique modifications to the original Norway yawl design by builders in other areas of Scotland and Ireland, eg. the Drontheim and Achill yawls.

More queries to follow in time.