boatspeed

Through measurement and observation I've found the highest speed I can obtain from my 16 ft planing dinghy is about two thirds of the actual wind speed. I'm curious about where this puts me in terms of efficiency--about average for a 16 footer--above average or below average ?

 

That question is similar to the ones like; how long is a string? There are 16 footers that do not go as fast as yours and there are a few that can go measurably faster. One of the major factors is the weight of the boat,crew, and whatever else you have in the boat. The type of sail rig determines speed somewhat but the area of the sail plan is probably more influential. The cut of the sail and your ability and skill for controlling the shape also plays into the equation. You can compare sailboats in a lot of different ways. One of the ways is to calculate the displacement divided by the sail area. That is something like the power to weight ratio of your Chevrolet Impala or your Kawasaki superbike.

If you are sailing in an 18 MPH breeze and the boat will make 12, you are doing OK. It is entirely possible for certain boat designs and layouts to do 18+ in an 18 breeze. Those are typically hot rod types, purpose built for the job, and almost always more physically demanding than something like....say...an O'Day Day Sailor, Wayfairer, or similar.

Are you the Sawmaster who posted some commentary while you were building your boat? That was some time back I think.

 

A 16' catamaran will do ~ 1.5 x the wind speed on a broad reach.

 

The point of sail makes a big difference. Downwind the boat speed will always be less than the wind speed. Reaching, it is possible to go faster.

 

thanks for the comments guys---I knew there were boats that were faster (and slower) than mine. For some reason I assumed there was some sort of mathmatical ideal maximum velocity that a planing MONOHULL of a certain length could reach (expressed as a percentage of wind speed).I am aware that displacement hull speed is length dependent and I thought there might be a similar limit for planing craft--a point at which (due to frictional resistance and other factors) a planing monohull reaches maximum possible speed(for a particular true wind speed) for its waterline length.I believe there is such a limit and I'm surprised that given the advanced state mathmatics no one has figured it out. I'm not talking about comparing apples to oranges i.e. hydrofoils to catamarans to skiffs--only interested in comparing planing monohulls of a particular length to other planing monohulls of the same length.

 

It depends on how long you time your speed and how you do it. Many years ago Rodney Pattinson sailed his FD at Weymouth speed week and only did 10+ knots over 500m. It is rare for any dinghy to average 15 knots for any distance (I have, on a course and timed between two navigation buoys) In part because of stability issues

What design do you have 49er or???

Richard Woods

 

Not a 49er but it is a Bethwaite designed Tasar. I'm sailing it single handed and under main alone. I've not considered the time element only peak speed. Ive not had it out in anything over 13 mph wind where I hit 9 mph for about 115 seconds--feels a little squirrley even at that speed. To hit 15 knots (17.2 mph) I'd have to be in about a 26 mph wind. Spooky!

 

I assume you have his book. Lots of performance data in that. A jib will certainly improve performance and in under 15 knots wind you should cope alone sssuming you are athletic

Richard Woods

 

Julian B is recorded as having hit 22.5 knots in a Tasar in 35 knots of breeze.

 

For how long measured how? Not disputing it. Just so many people overstate speed. I was sailing a catamaran a few weeks ago. We do 7 knots on one tack 8 on the other when measured by the log. The gps said 7.5 on both tacks. The discrepancy was because the log impeller was near the water surface so turned faster on one tack

Richard Woods

 

I'm using a Garmin bike gps and a watch. The 115 seconds is an estimate (that's why I said "about"115 seconds)--I failed to check my watch at the beginning of the gust--didnt expect it to last as long as it did but I've had numerous reaches lasting from a few seconds to a couple of minutes where I observed readings from 7.8 mph (6.7 knots) to 8.4 mph (7.2 knots) in only a 10 knot breeze. Every time,though, I seem to top out at around 2/3 wind speed --which may be the limit for this type of craft. I was just wondering if that puts the Tasar in the middle of the pack of similar sized planing dinghies or near the top. I cant imagine that there are too many other non-trapeeze dinghies of similar size that regularly EXCEED 2/3 wind speed although I would like to know if there are. I don't have the Bethwaite book but will order it. I assumed using a jib would increase top speed but not sure that would be prudent--I'm 63 years old and not as athletic as I used to be. My Tasar is number 166 -produced in the late 1970's. I sail on inland lakes and don't usually launch if the wind is 20 mph or more---so no illusions about setting any ultimate speed records for the Tasar. I will NOT be going out in 35 knots of breeze (or even 20). However, if anyone ever sponsored a contest for highest percentage of true wind speed attained, well ......

 

GPS speed is not accurate for speed over water surface, which is what really counts. Unless you correct for current, it is speed over a theoretical geoid surface.

 

The Tasar is underrigged compared to most dinghies (as is the Laser2). But is light and has an efficient hull form. Check the dinghy yardsticks to compare eg from the RYA in the UK. All available online and so are historical numbers

Richard Woods

 

thanks Gonzo---I wasn't aware fresh water inland lakes HAD currents.

 

You' welcome. All lakes have currents. Depending on the size, shape and depth they vary in speed.