Triple keels...why?

[dancrane]

Actually I was looking dreamily at the lines of the old Southerly 28, whose centerboard occupies a central keel-stub like a shallow fin, while shallow bilge keels prevent the boat rolling over when aground.

Later, bigger Southerlys had in the bottom of their hulls a large 'grounding plate' to protect both the leading edge of the raised centreboard and the central section of the hull itself from any hard knobbly crud which lies on the seabed where the yacht might be left to dry out...

...trouble is, the grounding plate doesn't cover the whole of the area at risk - so, letting a Southerly dry out, must require the seabed to be pretty smooth...

...in that respect, the Southerly 28 with her triple keels, plus a retracting keel for windward work, seems better able to dry out than her pure-centerboard sisters.

But which other yachts with triple keels, wouldn't have been better served by twin/bilge keels? Triples seem to suffer excessive drag for no obvious benefit.

 

[pvb]

But good things come in threes...

 

[Tranona]

The main champion of triple keels was Maurice Griffiths, although others such as Tucker also used them.

MG designs were from an era where heavy wood construction on a straight centerline using an iron keel was the norm. His sailing grounds on theater coast require drying out and although the keels sank in mud they did not dry out well on firmer ground, so he started adding bilge runners and then full depth bilge keels. His best triple keel designs such as Lone Gull 2 and Golden Hind had very firm bilges and he claimed that bilge keels reduced rolling downwind as well as improving windward performance as the leeward keel is immersed more deeply. He explains it all in detail in his various books. If I was not so comfortable sitting in front of the fire I would find specific reference. I have all of his books, most signed by him, but a nostalgia wallower like would do well to find your own copies.

One downside was that traditional wood construction could not support twin ballasts keels which have reduced the drag penalty of the Central ballast keel. The advent of GRP removed this constraint and although some early design such as the Trident had triples it became a dead end.

As a contrarian I have actually removed the bilge keels from my MG boat and deepened the Central keel as once I got a marina berth in the club the shallow draft and drying out became no longer important. Boat is much better as a result. The redundant bilge plates sat in my garden for 20 years until I sold them to an owner of a sister boat fireplace his corroded ones. Still got the old shallow barn door rudder if anybody wants it.

 

[charles_reed]

Actually I was looking dreamily at the lines of the old Southerly 28, whose centerboard occupies a central keel-stub like a shallow fin, while shallow bilge keels prevent the boat rolling over when aground.

Later, bigger Southerlys had in the bottom of their hulls a large 'grounding plate' to protect both the leading edge of the raised centreboard and the central section of the hull itself from any hard knobbly crud which lies on the seabed where the yacht might be left to dry out...

...trouble is, the grounding plate doesn't cover the whole of the area at risk - so, letting a Southerly dry out, must require the seabed to be pretty smooth...

...in that respect, the Southerly 28 with her triple keels, plus a retracting keel for windward work, seems better able to dry out than her pure-centerboard sisters.

But which other yachts with triple keels, wouldn't have been better served by twin/bilge keels? Triples seem to suffer excessive drag for no obvious benefit.

I think you may be jumping to conclusions - that the cast plate bonded into later Southerleys is there for "protection",
If you check with the naval architect who designed them, I think you'll find, he thought it was a far more convenient way of adding the required ballast - any "protection" was the hyper-active marketing splurge.
Having sailed fairly frequently in company with a number of early and more recent Southerleys I'd find it difficult to describe any of them as a "good sailer".

 

[Cloona]

a very sensible configuration.... the central keel needs a good forefoot to grip to windward and probably better than twin keels .... the bilge plates great for downwind and taking the ground - all giving a sensible draught .

a jolly good design for recreational sailing -

 

[dancrane]

Thank you for your informative contributions, gentlemen, particularly Mr T...may I offer proofreading services in return?

The worst thing about predictive computer systems is their bias towards US spelling. Amusing, though.

...sailing grounds on theater coast require drying out...I sold them to an owner of a sister boat fireplace his corroded ones.

 

[Wooden Boat Fittings]

The Yachting Monthly 3-Tonner (so-called because the design was entered by Alan Buchanan in their annual design competition, and won with it in 1948) could be mistaken for a Maurice Griffiths* design. She had a full-length displacement keel that she grounded on and two short steel bilge keels, almost as deep, that propped her up as she dried out. My Sanderling was such a design. She was wood (strip-planked) and had a long stringer inside the hull to which the bilge keels were bolted, and which distributed the loads from them.

There was 6" of drag on the keel, and total draft at the stern was only 2'-9", making her a lovely design for the shallow waters of Western Port, where I sailed her (waters similar in many ways to, say, the Walton Backwaters). The set-up worked very well for me, as I had a drying mooring outside my back gate where she took the ground twice a day, staying upright all the time --

... and I could navigate the many tortuous channels among the mudbanks (including the one to her berth) where a single-keel vessel simply could not go. Further, if I happened to take the ground on a falling tide I could sit it out in comfort until she floated off again. (It only happened once.)

The only thing about your original question Dan, is whether this type of design was what you meant by "triple keels".

Mike

* Maurice Griffiths was the Editor at the time, and I've always suspected Buchanan of designing a vessel to be as like an MG design as he could, in order to sway the judging panel. Buchanan was a very smart man as well as a first-rate designer.

 

[Tranona]

Yes. MG cajoled AB to do this design and several other small boats to promote the self build movement by offering plans through YM.

 

[aquaplane]

I have always thought of triple keels as the configuration used by Westerly in the '60s for the W25, Nomad, Windrush and others. They are twin keels with a massive skeg.

 

[Twister_Ken]

The redundant bilge plates sat in my garden for 20 years until I sold them to an owner of a sister boat fireplace his corroded ones.

Doncha' just love predictive spelling?

 

[Tranona]

Doncha' just love predictive spelling?

Yes makes one sound like John Prescott on a good day.