Sunday, January 20, 2013

Catching Up on Some Comments

For quite a long time now I've been unable to up-load photos to my blog without going through the process of putting them on a picture hosting site and them using the url of each individual photo. With the combination of Christmas/New Year, and a lot of building work to be done, I am afraid that posting has fallen behind. This is all done in my own time, and at my own expense, and it sometimes must take second place to paying work!

The computer people here will roll their eyes, but I've finally discovered that the picture loading problem was caused by incompatibility between the Microsoft Internet Explorer I had been using and the Google Blogger program which I use for the blog. I've now changed to Google Chrome for my internet work, and all seems to be working fine.

So I'm going to start off by answering a few comments that have been left on some of my posts.

Mr.Lillistone,I've followed your blog for a while,Thank you for your time,energy ,and expertise,It is appreciated by many!!! I know you have built both Michalak's Mayfly and Redmond's Bluegill,I'm considering building either one and would like your professional opinion.Do you think the Mayfly leeboard and balanced lug sail plan could be used on the Bluegill ,if the sail is properly positioned over the leeboard,and leeboard is centered on beam?I would like the open cockpit the leeboard affords.Any info. Would be appreciated thanks in advance ! Jerry Fehn on Reality

The Bluegill we built, showing her centreboard case
Jerry's comment refers to a matter which has nagged at me for many decades. A centreboard is convenient to use and is to a large extent self-tending i.e. put it down and if you are too busy for detail work, just leave it down until it hits the bottom coming home. On the other hand, leeboards need to be handled from tack to tack because, as their name suggests, they only work when set on the leeward side of the boat.

A raised leeboard on a Dutch Yacht (taken from http://www.leeboards.com/)
That is me sailing my Bolger Nymph a long time ago. I had fitted her with leeboard for experimental purposes, but in this photo they are both raised as the boat is running downwind.
My understanding is that leeboards originated in China, along with such things as stern-mounted rudders, centreboards, and watertight bulkheads to name just a few Chinese nautical inventions/developments. Leeboard use has been widespread, but most people associate them with Dutch, German, and British sailing vessels.

This shows a typical lowed position for a leeboard.

Leeboards may appear untidy to some eyes, and to need handling from tack to tack, but they are highly efficient. Frequently the boards are angled away from the hull to allow a clean passage of water between the hull and the board so as to prevent excessive drag. This feature also means that as the boat heels, the board becomes more and more vertical - which is just the opposite of what happens with a centreboard or fixed keel. Not only does the board become more vertical, but it also works from the surface of the water, whereas the centreboard only works from where it exits the bottom of the boat. This has the additional benefit of allowing leeboards to operate effectively in a partially raised position in shallow water, and not extend below the bottom of the boat.

A Bolger Black Skimmer sailing with her board partially raised. The board is effective, but does not extend any deeper than the hull, if at all. (Photo from Woodenboat Magazine)
An overlooked plus with leeboards is that because they each operate operate on different sides of the boat (in their normal form anyway - more on that later) the sectional shape of the boards can be asymmetrical, allowing the board to lift the boat to windward at a reduced angle-of-attack in comparison with a board which has a symmetrical foil shape. The boards should have a flat face away from the boat and a cambered face towards the boat.


An Otter II with both of her leeboards raised while on her shallow water mooring. Note how the owner has the leeboards on the incorrect sides. The cambered section should face the hull, so in this case the starboard board is mounted on the port side, and the port board is mounted on the starboard side!
You may wonder why leeboards frequently have a tear-drop or triangular shape, with the widest part down low. This is because they are surface-piercing foils, and the inverted taper shape helps to reduce air-ingestion  on the low-pressure side of the board.

Despite the visual and actual clutter of the boards, they have some potent advantages in addition to the ones already mentioned: -

  • the interior of the boat is totally free of the intrusion of a centreboard case; and
  • the bottom of the boat is stronger without a centreboard slot; and
  • there is no centreboard slot to get jambed up with mud, stones, shell grit and sand - which therefore leads to the centreboard being jambed.
It is possible to mount the leeboard to one side of the boat only, but for that to be effective, the board must be prevented from bending away from the side of the hull when it is on the up-wind side. This can be done using a 'dagger leeboard' ( which I guess would be a 'weatherboard' on one tack) where a variety of methods are used to hold the board in place. Alternatively, you can have a pivoting 'lee board' as developed by Jim Michalak and others. In this case, the board is held parallel to the side of the boat by a pivot bolt and wooden guards and/or slots, but the board is free to pivot in the vertical plane. Although simple in concept, great care is required to ensure that all of the pivot locations and guard angles are absolutely correct.


Above two photos show the Michalak Mayfly 14 pivoting leeboard
Here is the finished boat
Note the completely unobstructed interior....
...the very simple raising and lowering gear...
...and the lower guard with the pivot bolt going through (the piece of unpainted wood is positioning piece on the trailer)
Now, to finally get to Jerry Fehn's question - Yes, it would be possible to mount a pivoting leeboard on Bluegill in place of the centreboard and case, but great care needs to be taken with the positioning of the board relative to the centre-of-area of the sail, and also with the geometry of the pivot point and the guards so that the board remains parallel with the centreline of the boat.

Having said all that, the first person who should be consulted would be Steve Redmond, the designer of Bluegill. As has been said many times in the past, no-one should alter the design of a boat without getting input from the original designer. This is not grandstanding at all - it is simply that the designer should have put a lot of thought into the design, and there may be elements there which are not obvious to the casual observer.

My recommendation would be to build something like Mayfly 14 if sailing is the most important aspect of operation. She sails superbly in my experience, and the shape of the hull is optimised for sailing whereas Bluegill's hull is a deliberate attempt to produce a hull that will row, sail, and operate as a planing powerboat.

4 comments:

  1. Hi Ross- Love the post on leeboards. I built the Black Skimmer in the photo you used , in the early 80's- great boat for shoal waters. I knew Phil Bolger, built a few of his designs. I like a lot of your designs, they have the essential simplicity that I feel is necessary on the water.

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  2. "As has been said many times in the past, no-one should alter the design of a boat without getting input from the original designer." That's something Philip C Bolger also had strong opinions about. Change his design work a bit and he'd likely disown it, saying it was now the design of the builder not his.

    Well Ross, that pictured Otter II features deviations from Bolger's design. Of significant relevance is that of the assymetric leeboard. Although Bolger drew assymetric boards for a few particular, and noteably larger voyaging boats, he eschewed the idea in print as not worth the bother and trouble, and drew the Otter II with symetrical leeboards. Along that line he wasn't too bothered at all with raising the windward board on alternate tacks, as is once more evidenced here on Otter II by his giving her the best method of hanging leeboards he knew at the time - a method that allowed the windward board to "broken wing" without complications or bother.

    It is indeed a very nice looking boat, that pictured cat type leeboarder. One of your fine builds? Is that photo taken at Moreton Bay?

    By the way, they didn't also go for leeboard toe-in did they? :-0

    Graeme

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    Replies
    1. There is no alteration of design to Otter II, all is built as per Bolger drawings. Both leeboards are identical, with no cambering. The cross section is symmetrical. Leeboards are made of two sheets of ply with sharpened edges. Yes, the leeboards go broken wing under way, as there is no lift generated by the cross section. They are mounted and pivot at the top on a shaft. No, there is no toe-in, the shaft is exactly fore and aft. The working leeboard is held against the hull by pressure generated by the leeway only.

      The Owner

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  3. Got any more pics of Otter II?

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