Wednesday, June 29, 2011

Comment regarding "Photos of a good flat-bottomed skiff"

Graham has written with a comment about leeboards: -

Nice pics. My life seems to be one long series of overdue jobs, so I know what a relief it is to be back on task!

The external chine logs I don't mind so much, but the leeboard?? I know there are some really good practical reasons for going down that path, and I know that Phil Bolger was a great advocate of them, but they take some getting used to.

Apart from the increased internal space, do you think you could just remind me what the benefits of a leeboard are; especially when used in conjunction with a flat bottomed hull like this one.

Well, I'm not an expert on the subjuect, but the most obvious advantage of leeboards is exactly what Graham has pointed out - less clutter inside the part of the boat in which people want to sit. Now, having a centreboard case in there with you is not necessarily a bad thing. I've found a case to be a great way to brace one's feet; to bundle people away from each other when sleeping; and to use as a sort of improvised set of hiking straps by hooking the soles of your feet under the upper external framing of the case while hiking out.

Another advantage of leeboards is that they are providing lateral plane from the surface of the water down to their tips, rather than from the bottom of the centreboard case to the tip. The problem there is that I suspect that the "end plate" effect of the bottom of the hull over the centreboard more than makes up for the increased effective area of the leeboard.

But despite all of that (including arguements about better hull strength without a centreboard slot), there is one overwhelming practical advantage of leeboards for a cruising dinghy, and that is avoiding the plague of having sand and shell-grit pumped up into the centreboard slot while the boat is pulled onto the beach with wavelets surrounding her. That is the reason why my centreboard designs have a positive method of forcing the centreboard down, rather than just relying on a block of ballasting lead in the board - a jambed board is a potentially serious problem, particularly when leaving a lee shore - you must be able to get the board down quickly, and the combination of sand and shel-grit inside a case is a serious problem. It is also a very good arguement in favour of a dagger board rather than a pivoting centreboard.

I've been having an interesting discussion with a fellow in Maine about the effectivness of long, shallow keels. He sails a Phil Bolger Oldshoe and I occasionally sail a Bolger Micro - both of which have long, shallow keels. Both of us have been pleasantly surprised by just how effective these keels are - despite what the theorists will tell you. If you get the chance, read Arthur Ramsome's books in the Swallows and Amazons series (I read my first one at about eight years of age, and I'm still reading the twelve-book series on a regular basis - they are that good), where he describes Swallow, a 14 ft clinker sailing dinghy with a shallow keel.
Here is me sailing along happily in my leeboard-equipped Bolger Nymph. The boat is on a run, with the boards raised, but I can assure you that they worked very well indeed!
This jpg shows my Whimbrel design (17ft x 6ft 9in), which incorporates leeboards for many of the above reasons. These plans are quite detailed, and although close to being finished, will still be a month or so. Too much work on my plate, and only one person to do the jobs!


  1. She sure is pretty! And I think just the design I have been hoping to find. I look forward to reading more about Whimbrel.

  2. Thanks for the comment. I really like Whimbrel myself, and the plans themselves are close to being finished, but instructions to come. She is of stitch-and-glue construction, and is very robustly built in comparison with many of the flimsy designs around. The scantlings are all based on the recommendations of Dave Gerr, and she will be a tough little boat. The base of the mast runs up through a slot in the foredeck (like a centreboard case). Internal volume is similar to "Micro" - probably just a bit larger - but she draws very little. Current consideration is whether to incorporate ballast - if so, water or lead? I like un-ballasted boats myself for this application.

  3. Look forward to seeing the finished Whimbrel, especially the accommodations and whether she does incorporate ballast.

    Gary Blankenship

  4. Gary,

    I have a plan to build a scal model as soon as I can, using scale thickness plywood and timber (to the correct density) and to carry out stability testing using scale weight items such as outboard, stores, sails and persons. I've done this sort of thing before, having been influenced by the writing of Weston Farmer.

    I find the boat interesting for a number of reasons, and I have a few options in mind, such as a Birdwatcher-style slot-top and maybe a Micro-style cockpit as an option rather than the conventional foot-well currently on the plans.


  5. Gary,

    If you get a chance, could you please send me an email to r.lillistone(at) ? I've lost you address in a computer change, and I'd like to send you some pdf files for interest. Thanks,



  6. Ross - I have often thought that stubby little bilge keels combined with leeboards might be just the ticket. The bilge keels could have through holes or threaded inserts in them. When ultimate stability in heavy weather was called for, a long heavy steel plate could be bolted to each keel. In light weather, etc the steel plates could be left off. And the little bilge keels would more or less allow her to sit level when the tide is out. If designed just right the boat could travel on a flat trailer or a traditional boat trailer. The steel plates could just stay right on the trailer in position to be bolted on or off as needed - no lifting or grunting required.

    I am not any sort of designer or engineer but I have often thought that this sort of arrangement would offer lots of flexibility and simplicity and be budget friendly.

    Feel free to shoot holes in my thoughts - I am just always dreaming of my ultimate boat on a budget.
    Thanks Ross!

  7. Btw -kineticj =Mike the stubby bilge board suggestion. I have not mastered posting from my cell phone.

  8. Mike, Thanks for the comment, and sorry for the delay in posting a reply. Bilge keels are very attractive for the reasons you mention - sitting upright on the bottom when grounding out and also allowing a boat to be pulled up onto a flat-bed trailer.

    The problem for me is that I can't get past my concern that the flow of water around the bilge section of a hull is almost never parallel with the centreline of the boat, and therefore the bilge keels generate drag out of proportion to their surface area. I don't know much about the hydrodynamics, but I will try to write a post about the idea.