Bilge keel draught when heeled

[B27]

...
If one does produce a bilge keeler, it has to prove itself capable of a decent turn of speed, one might think.

Since people keep buying cruising yachts with lumpen great 3 blade fixed propellors, I surmise that a fair chunk of the market is not all that concerned about performance under sail.

 

[johnalison]

I never had any intention of serially scrubbing during the season. When I was working it would have meant a lost weekend, when I was already doing a 1:2 rota. When I retired it was unnecessary. Three months summer cruising, on the move about every other day, kept the bottom clean enough, and if we went to the Baltic and returned through Dutch canals we were as clean as when we started. More recently I have launched late and just put up with losing a little speed, though this year was pretty good, as I was only down less than 1/4 knots when motoring. I can get a pressure wash against a wall locally for £45 but it is quite a faff and hardly worth it.

 

[Pete7]

Since people keep buying cruising yachts with lumpen great 3 blade fixed propellors, I surmise that a fair chunk of the market is not all that concerned about performance under sail.

Au contraire, we do try to sail quickly and spend time fiddling with the sail shape learning as we go. Also pressure wash before major trips away. Like John, a trip up a river for a couple of days helps clean the hull at the expense of a tide mark from rivers like the Dart.

A folding prop to replace the fixed two blade, but at £1500, it's a little off putting. Also needs to be a left handed prop buy if we re-engine then a right handed prop would be needed. Tricky. Sails are reasonably new and looked after, but along the south coast the biggest gain is using the tides properly even if that means departing at 1am for a night sail as we did leaving Portland last month.

We also do an annual spring clean and weight saving review to see what we can take home or get rid of. The club has a corner for "freebies" which we have benefited from and equally donated surplus items that always seem to go quickly.

 

[Frogmogman]

However, I believe that some that try to emulate performance of lifting & fin keels do make bilge keelers. RM comes to mind. Are they still in production after the last buyout following the financial collapse a few years ago?

Yes, RM are still in business, and are now in safe hands as part of the Grand Large yachting group, owners of Outremer, Allures, Garcia and Gunboat. The financial collapse was due to inadequate capitalization meeting a cash-flow problem caused by the collapse of the subcontractor who moulded the decks. They had a 2 year order book at the time.

The narrow chord with bulb twin keels on the RM range are very effective; not quite as good to windward as their single keel models, but not far off. When the boat is heeled, the leeward keel is near vertical, providing good lateral resistance and directional stability, while the windward one provides good righting moment from a nice chunk of cast iron stuck to windward at the end of a long lever. Less draught than the single keel version and they take the ground without fuss. Perfect for tidal waters. What’s not to like ?

 

[B27]

My point was more about people who buy new boats. A folding prop is not a huge part of the cost of your typical 34ft BavBenneau. People save a few hundred pounds and prioritise astern performance in the marina over sailing efficiently. These people are not dismissing twin keels on performance grounds, they are buying what the mass builders are selling.
Unfortunately us buyers of quality used items have our choices made for us by the buyers of new items.

There are lots of secondhand LH folding props out there, from boats re-engined to Beta I suspect.
They do have wearing parts, so take care with 'bargains', but a lot of people are probably hoarding good props!

 

[John_Silver]

Yes, RM are still in business, and are now in safe hands as part of the Grand Large yachting group, owners of Outremer, Allures, Garcia and Gunboat. The financial collapse was due to inadequate capitalization meeting a cash-flow problem caused by the collapse of the subcontractor who moulded the decks. They had a 2 year order book at the time.

The narrow chord with bulb twin keels on the RM range are very effective; not quite as good to windward as their single keel models, but not far off. When the boat is heeled, the leeward keel is near vertical, providing good lateral resistance and directional stability, while the windward one provides good righting moment from a nice chunk of cast iron stuck to windward at the end of a long lever. Less draught than the single keel version and they take the ground without fuss. Perfect for tidal waters. What’s not to like ?

In a similar vein; here is the VPP data for the RM 1070+. (Which I posted on the-other-bilge-keel-thread). The tables show VPP numbers for their RM1070+. A modern 35 footer which is available in Bilge keel (Biquille), Fin (Monoquille) and lift keel (Quille Relevable) configurations. The bilge keels in question are bulbed, high aspect designs.
The third table gives the %age difference in performance, between the fin/ lift keel (first table) and bilge keel (second table) versions, over the full range of wind angles and strengths. The performance of the lift keel and fixed fin are said to be identical. Broadly, the lighter the wind and the tighter its angle, the greater the advantage of the fin(s). 10%, at its height. Diminishing to 0% as the breeze comes onto, and aft of, the beam.
The RM range starts at 30 feet and goes up to 45. All models available with fin, lift or bilge keels."

 

[B27]

In a similar vein; here is the VPP data for the RM 1070+. (Which I posted on the-other-bilge-keel-thread). The tables show VPP numbers for their RM1070+. A modern 35 footer which is available in Bilge keel (Biquille), Fin (Monoquille) and lift keel (Quille Relevable) configurations. The bilge keels in question are bulbed, high aspect designs.
The third table gives the %age difference in performance, between the fin/ lift keel (first table) and bilge keel (second table) versions, over the full range of wind angles and strengths. The performance of the lift keel and fixed fin are said to be identical. Broadly, the lighter the wind and the tighter its angle, the greater the advantage of the fin(s). 10%, at its height. Diminishing to 0% as the breeze comes onto, and aft of, the beam.
The RM range starts at 30 feet and goes up to 45. All models available with fin, lift or bilge keels."

I think if you look at a typical 'English Bilge Keeler', it will have shallower draft and less righting moment than the fin model.
I suspect we reef earlier than some 'equivalent fin model'.
I also think the above is all about flat water, a shallow draft boat with less righting moment may need to be sailed more conservatively as the sea-state roughens.

 

[B27]

Au contraire, we do try to sail quickly and spend time fiddling with the sail shape learning as we go. Also pressure wash before major trips away. Like John, a trip up a river for a couple of days helps clean the hull at the expense of a tide mark from rivers like the Dart.

A folding prop to replace the fixed two blade, but at £1500, it's a little off putting. Also needs to be a left handed prop buy if we re-engine then a right handed prop would be needed. Tricky. Sails are reasonably new and looked after, but along the south coast the biggest gain is using the tides properly even if that means departing at 1am for a night sail as we did leaving Portland last month.

We also do an annual spring clean and weight saving review to see what we can take home or get rid of. The club has a corner for "freebies" which we have benefited from and equally donated surplus items that always seem to go quickly.

It occurs to me that because my boat had been re-engined with nearly twice the power, it was dragging a bigger prop through the water. Also the choice of gearbox ratio will affect the blade area and pitch and hence the prop drag. Maybe Mr Previous Owner found the boat was OK with the fixed prop on its original 1GM, so went with a fixed prop with the new engine. But the new boats people are buying recently tend to have bigger engines relatively, hence big fixed props. They also tend to have a lot more LWL, which means they are naturally quicker though.

As you say, there is more to making progress than raw boat speed, tides and wind strategy matter.