Boat speed under sail, what should I expect?

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Trop Cher

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I sail a awb of 40 feet. I usually get her up to seven knots quite easily say in a F4/5 and I'm chuffed when I get over eight knots, top speed so far is 8.7 knots, this is boat speed using the log not gps.
I was recently talking with someone who sails a 27 ft boat and said that he regularly gets over nine knots. I suggested that that must include tide, but he said no, that was from his log.
Now either I'm doing something wrong or he needs to recalibrate his log?
What sort of speeds should I expect?
 
Trop Cher said:
I sail a awb of 40 feet. I usually get her up to seven knots quite easily say in a F4/5 and I'm chuffed when I get over eight knots, top speed so far is 8.7 knots, this is boat speed using the log not gps.
I was recently talking with someone who sails a 27 ft boat and said that he regularly gets over nine knots. I suggested that that must include tide, but he said no, that was from his log.
Now either I'm doing something wrong or he needs to recalibrate his log?
What sort of speeds should I expect?
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In his dreams. Only way he could achieve that is if the boat is light enough to surf, but such speeds are not sustainable. His operating range is sub 6 knots because of waterline length.

Your speeds are just what one would expect for your boat.
 
There's more to it than just length. I used to crew on a 24ft sportsboat which readily planed downwind and occasionally hit 15 knots.
 
Everybody lies about their boat speed. It's a fact of life, like fishermen and their catches. The usual reason is using GPS speed in their boasts. I can say that my best speed in our 34 was 11.5 kn. but I will add that I knw that my log overreads at higher speeds.
 
DJE said:
There's more to it than just length. I used to crew on a 24ft sportsboat which readily planed downwind and occasionally hit 15 knots.
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If he had such a sport boat he would be claiming far higher speeds than 9 knots.

As suggested claimed speed would be surfing or speed over the ground with a favorable tide. I regularly exceeded 9 knots over the ground going through Just on a spring tide in my heavy old 26'.
 
Trop Cher said:
I sail a awb of 40 feet. I usually get her up to seven knots quite easily say in a F4/5 and I'm chuffed when I get over eight knots, top speed so far is 8.7 knots, this is boat speed using the log not gps.
I was recently talking with someone who sails a 27 ft boat and said that he regularly gets over nine knots. I suggested that that must include tide, but he said no, that was from his log.
Now either I'm doing something wrong or he needs to recalibrate his log?
What sort of speeds should I expect?
Click to expand...

Are you measuring this upwind, down wind or reaching
9Knots is possible in a smaller boat for short bursts but not long distance
Certainly I know of sub 30ft boats that plane at 15Kts ( mini transats for example)so your friend may not be untrue.

What you need is the polar diagram for your boat then you compare your performance with that. It will tell you how well you are sailing
 
Daydream believer said:
Are you measuring this upwind, down wind or reaching
9Knots is possible in a smaller boat for short bursts but not long distance
Certainly I know of sub 30ft boats that plane at 15Kts ( mini transats for example)so your friend may not be untrue.

What you need is the polar diagram for your boat then you compare your performance with that. It will tell you how well you are sailing
Click to expand...

Yes you will get 27ft boats that will do 9 knots but if it does 9knts it will have a planing hull and would achieve more than 9knts so his dream speeds would be into double figs.
 
As a rough rule of thumb, for an AWB, you would use the formula Speed {knots} = 1.14 . sqrt(length{feet}).

Thus for a 36' Jeanneau you get a speed of 6.84 knots before you start planing / surfing down the back of waves / heeling (and so changing the hull profile).

The fundamental reasons for this (for displacement yachts) is that as the yacht moves faster forward, the trough from the bow wave will move further towards the stern - just imagine looking side-on to a yacht as it sails (motors even) by - the trough is probably 80% of the length back from the bow. This will eventually cause the yacht to pitch upwards by a degree or two, thus creating drag and so limiting speed (and so putting more power in doesn't help - other than causing a broach or rounding up). Clearly this is length dependent and also dependent upon the hull shape. The 1.14 in my example is a typical number (and probably outdated for a modern Jeanneau) every yacht design will vary slightly, but hopefully you get the picture).
 
marklucas said:
As a rough rule of thumb, for an AWB, you would use the formula Speed {knots} = 1.14 . sqrt(LWL feet}).

Thus for a 36' Jeanneau you get a speed of 6.84 knots before you start planing / surfing down the back of waves / heeling (and so changing the hull profile).

The fundamental reasons for this (for displacement yachts) is that as the yacht moves faster forward, the trough from the bow wave will move further towards the stern - just imagine looking side-on to a yacht as it sails (motors even) by - the trough is probably 80% of the length back from the bow. This will eventually cause the yacht to pitch upwards by a degree or two, thus creating drag and so limiting speed (and so putting more power in doesn't help - other than causing a broach or rounding up). Clearly this is length dependent and also dependent upon the hull shape. The 1.14 in my example is a typical number (and probably outdated for a modern Jeanneau) every yacht design will vary slightly, but hopefully you get the picture).
Click to expand...
fixed that
 
M
marklucas said:
As a rough rule of thumb, for an AWB, you would use the formula Speed {knots} = 1.14 . sqrt(length{feet}).

Thus for a 36' Jeanneau you get a speed of 6.84 knots before you start planing / surfing down the back of waves / heeling (and so changing the hull profile).

The fundamental reasons for this (for displacement yachts) is that as the yacht moves faster forward, the trough from the bow wave will move further towards the stern - just imagine looking side-on to a yacht as it sails (motors even) by - the trough is probably 80% of the length back from the bow. This will eventually cause the yacht to pitch upwards by a degree or two, thus creating drag and so limiting speed (and so putting more power in doesn't help - other than causing a broach or rounding up). Clearly this is length dependent and also dependent upon the hull shape. The 1.14 in my example is a typical number (and probably outdated for a modern Jeanneau) every yacht design will vary slightly, but hopefully you get the picture).
Click to expand...

Don't they quote 1.3 times now but principle is right.
 
How can one explain the speed of the MacGregor 65 and 70? Double figured multi-hull speeds are reported all the time with research on said model. :ambivalence:
 
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