Hull speed?

[dunedin]

Bulbous bows allow for an increase in speed of about 15% in a very narrow relative speed range of between 0.6 and 1 ( Sqr root DWL x speed factor). As sailing yachts operate at the variance of the wind, a bulbous bow makes no sense. Freighters tend operate pretty much precisely in this speed range.

….

One yacht design tried the bulb bow - Coronet Elvstrom 38 - Coronet Elvestrom 38 for sale Spain, Coronet boats for sale, Coronet used boat sales, Coronet Sailing Yachts For Sale Coronet Elvstrom 38 - Apollo Duck

Think there is one at Largs. No idea if works or not, but must catch a lot of kelp and pot buoys

 

[Chiara’s slave]

One yacht design tried the bulb bow - Coronet Elvstrom 38 - Coronet Elvestrom 38 for sale Spain, Coronet boats for sale, Coronet used boat sales, Coronet Sailing Yachts For Sale Coronet Elvstrom 38 - Apollo Duck

Think there is one at Largs. No idea if works or not, but must catch a lot of kelp and pot buoys

I doubt bulb bows will catch on in the racing community.

 

[Laminar Flow]

Yes, the Elvstrom is a motorsailer and the bow's performance advantage is (near enough exactly) between 3 and 5 kts. If you are happy pooteling along at 4 kts (average) then that is ok.

There are other options. The CP on our tub is 0.6 with an optimum relative speed of 1.25. This CP offers a 20% reduction in resistance at this speed over a lower CP of say 0.55, which would be more common. The penalty for this at lower speeds is easily overcome with more sail; the reduction in windward capability I can live with. It also goes a long way in explaining why such a supposedly ungainly craft as ours, can indeed sustain speeds of well over 8 kts under sail. This, in spite of a D/L of 360.

 

[Chiara’s slave]

Yes, the Elvstrom is a motorsailer and the bow's performance advantage is (near enough exactly) between 3 and 5 kts. If you are happy pooteling along at 4 kts (average) then that is ok.

There are other options. The CP on our tub is 0.6 with an optimum relative speed of 1.25. This CP offers a 20% reduction in resistance at this speed over a lower CP of say 0.55, which would be more common. The penalty for this at lower speeds is easily overcome with more sail; the reduction in windward capability I can live with. It also goes a long way in explaining why such a supposedly ungainly craft as ours, can indeed sustain speeds of well over 8 kts under sail. This, in spite of a D/L of 360.

Some of the most unlikely craft are surprisingly nippy. All down to the design brief. We too overcome our light air deficit with sail power. A tall rig, roachy square top main and big kite, and a code 0. We need 8kn of wind to plane. Our design trade offs are limited accommodation and a final limit to ultimate stability. Horses for courses. A 1/4 tonner usually drags a massive sternwave to show off it’s underwater profile. Plus that tiny transom Smaller than ours, with the ability to turn on a sixpence, whether you intended to or not. Quick in medium airs though.

 

[ProDave]

Our HH23 crossed the finish line on Saturday at 6.4 knots, which is above theoretical hull speed. Probably 15 knots of wind then sailing close to the wind. Much above that we are putting a reef in.

Down wind on Sunday with spinnaker up in very light winds only managed 5.3 knots max.

 

[MisterBaxter]

From memory the idea behind the bulbous bow on the Elvstrom was to give lower fuel consumption at a specific cruising speed that would also give the best mpg for the hull and engine, so as to give a much longer range under power without needing to carry as much fuel. Possibly a useful idea for boats that cruise among all the little islands in a Scandinavian summer.

 

[Supertramp]

From memory the idea behind the bulbous bow on the Elvstrom was to give lower fuel consumption at a specific cruising speed that would also give the best mpg for the hull and engine, so as to give a much longer range under power without needing to carry as much fuel. Possibly a useful idea for boats that cruise among all the little islands in a Scandinavian summer.

It's a good idea for a cruising boat that may motor for significant periods. There is a case for a cruising yacht to be a different balance between efficient motoring as well as sailing, not just a good sailing performer with an add on engine.

I have a suspicion that many people on a month or two sailing in UK waters will use the motor more often than might be imagined. I do.

Returning to the thread, I struggle to exceed hull speed in my motorsailer, even with a relatively yacht shaped hull and decent sail area. To get beyond it (6.5 knts) would involve carrying a lot more sail than I am comfortable with, or comfortable getting furled or down.

 

[Chiara’s slave]

It's a good idea for a cruising boat that may motor for significant periods. There is a case for a cruising yacht to be a different balance between efficient motoring as well as sailing, not just a good sailing performer with an add on engine.

I have a suspicion that many people on a month or two sailing in UK waters will use the motor more often than might be imagined. I do.

Returning to the thread, I struggle to exceed hull speed in my motorsailer, even with a relatively yacht shaped hull and decent sail area. To get beyond it (6.5 knts) would involve carrying a lot more sail than I am comfortable with, or comfortable getting furled or down.

Our attitude to sail carried is certainly different when cruising rather than racing. Even though it can have a big effect on speed for us. Spinnaker particularly is a light wind only cruising sail. Why bust a gut? Though clearly some might well wonder why we ever do at all, just for the sake of a little bit of tin.

 

[Supertramp]

Our attitude to sail carried is certainly different when cruising rather than racing. Even though it can have a big effect on speed for us. Spinnaker particularly is a light wind only cruising sail. Why bust a gut? Though clearly some might well wonder why we ever do at all, just for the sake of a little bit of tin.

I met a cruising Dragonfly in Scotland. They had covered in one day what had taken me 2 full days! I could see the appeal and the cruising opportunities of not having a "speed limiter" hull form.

I later retired to my ensuite double cabin....

 

[Chiara’s slave]

We have twin on board showers. The trampolines.

 

[onesea]

Our attitude to sail carried is certainly different when cruising rather than racing.

Racing I set sail for the lows and trim through the gusts.
Cruising I set sail for the gusts, and cruise through the lulls.

Unless a boat tries overtaking me.