Photos of a Good Flat Bottomed Skiff

Back in April I wrote two posts about flat-bottomed sailing and rowing boats (see Discussion About Flat-Bottomed Boats and Sharpie Hulls and Fine Sections ).

Things have been pretty hectic at our place since the disasterous flash-flooding which hit our area on January 10, 2011, but over the last few weeks Ive been getting back to work on some over-due jobs, one of which is a nice flat-bottomed skiff for a customer in Brisbane. She is a Jim Michalak-designed Mayfly 14 and is a good example of a well-designed flat-bottomed hull. The point to note is the relationship between the curve (or rocker) of the bottom when viewed in profile, and the curve of the topsides when viewed in plan-view. These two shapes, in combination, determine the chine-line, and the the flow of water around that chine. The aim is to reduce cross-flow to a minimum in order to minimise eddying.

A nice, simple boat, showing the pivoting leeboard, centreline hatches, and external chine log.

Many people find external chine logs difficult to accept, but they have some advantages. They are much easier to install on a boat which isnt built on a strongback, avoiding compound bevels and determination of length. In addition, they provide good protection to the chine, which is somewhat vulnerable on a flat-bottomed boat. Phil Bolger had a theory that if the hull was properly shaped, an external chine log may reduce drag, by delaying the point at which cross-flow occurred. In addition, I guess that they provide a bit of extra lateral resistance, which is good in a sailing boat.

Brutally simple pivoting rudder design which requires only one rudder cheek. The key is the amount of blade above the pivot point, as it provides support to the blade regardless of which tack the boat is on. The patch at the bottom of the blade is where Ive cast in a block of lead to sink the blade. It is covered with a small patch of 200gsm/6oz glass to prevent cracking between the lead and the plywood. The white is epoxy and sanding filler. 

Very simple, but rugged, mast step and mast partner, well braced by framing on the other side of the bulkhead.

Close-up of the mast step showing the very necessary drain hole to get rid of water in the step. This is all a bit rough at this stage, still waiting for some clean-up and fairing work.

Close-up of the external chine log, rounded over on both edges, and showing how Ive brought the epoxy/glass bottom sheathing around the bottom edge and up over the chine log. This is to protect the vulnerable edge grain of the 1/2" plywood bottom.

Outer stem made from a superb piece of Celery Top Pine from Tasmania. Hard, dense, and strong. Still waiting for finishing work and fairing.

Close-up of the external gunwale/sheer clamp, laminated from two beautiful pieces of Silver Quandong. Note how in a simple boat like this, there are plenty of places where the edge grain of plywood planking is vulnerable - this needs to be considered, with action taken to protect the edge. The edge of this plywood will be treated with three or four soaking coats of epoxy prior to being painted, but even then it will have to be watched in service.

Detail of the corner joints in the hatch framing. Once again, Silver Quandong

The single-sided pivoting leeboard allows for a clean and open interior. Although simple in concept, the leeboard design requires great attention from the builder when fabricating the leeboard upper and lower guards, so that the board is absolutely parallel to the centreline of the boat. Trickier than it looks!

A nice, simple, rugged boat. The external stem cap is yet to be trimmed, and at this stage Im planning on finishing it off with a Jonesport Cleat.

So, there you have a nice little boat. But you dont get something for nothing. These boats might be easy to build, but they consume large numbers of silicon bronze screws, and the structure is quite heavy. However, she should give long and trouble-free service, given that she is painted properly (she will be) and stored properly

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More photos of Fleet the planing version of Flint

The first example of Fleet, the planing hull version of Flint is getting much closer to launch day. In fact she has already been in the water to allow the marking of the waterline in preparation for the painting of the boot top - empirical data gathering!

Painting has gone ahead at a great rate, using the skills of people who normally apply coatings to aeroplanes and helicopters.

First real opportunity to view the hullform in the flesh.

 The hull shape is similar to the designs of the late William H. Hand, said to have been the inventor of the vee-bottomed motorboat. What made the William Hand designs significant was the way they would handle well at lower speeds when throttled back. Weston Farmer said of them, "They were steerable throughout their entire range of speed in following seas. The full planing boat is a dog in this department. Unless they are banging along full bore, you cannot steer them. And full bore in some seaways with this type of boat, demands Polident for the helmsmans teeth and metal brassiers for the ladies." ("From My Old Boat Shop" International Marine 1979.) Now, I think planing hull design has come some way since Weston Farmer formed his opinion, and there are some very fine designs around for full planing hulls, but the fact remains that for moderate planing and semi-planing speeds, a long, narrow Hand-style hull can be superb.

Getting ready for a trip down to the boat ramp for waterline marking. Gunwales are masked, as they will be finished bright using Deks Olje #1

First splash. Chines dont even touch the water when light. I hope that with a single oarsman on the forward thwart, the boat will be reasonably pleasant to row, even though she is a planing hull. Trim will be everything with passengers aboard.

25 litres of water in the aft well to represent the outboard and fuel, plus two people. The fellow on the helmsmans thwart is quite light, but the trim is very close to that predicted on the plans.

After the floatation tests, marks were made to allow masking-off for the boot-top.

Note the chinagraph pencil marks at the base of the stem.

Boot top masked ready for topside painting

Here you can visualise the fine, sharp lines up forard - she should give a smooth ride at moderate speed in a chop.

Almost ready for the water - just the oiling of the gunwales and breakwater/coaming to go. Test motor will most likely be a 6HP 4-stroke, but that is to be confirmed.

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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 dont 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, Im 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. Ive found a case to be a great way to brace ones 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.

Ive 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 Ramsomes books in the Swallows and Amazons series (I read my first one at about eight years of age, and Im 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!

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