RE: Spray rails on Supercat 17

Technical discussion of ARC products
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alexfoxfox
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Joined: July 3rd, 2013, 12:06 pm
Boat Make/Model: Supercat 17

RE: Spray rails on Supercat 17

Post by alexfoxfox » October 9th, 2017, 2:27 pm

Dear All,

After 3 years of happy sailing I am in the process of fairing and re-gelcoating of my 1983 Supercat 17. There is a pretty substantial amount of work as it has developed pretty big "waves" on the hull surfaces between bulkheads over the years (bought it this way). As the work will continue for a few months through the winter I was thinking that maybe it is the right time to add the spray rails (analogous to the ones used on Hobie Wild Cat) provided it is worth the effort.

So my question this:
Did anybody tried or thought about using such spray rails and if yes are there any recommendations or thoughts about the width , height and longitudinal position of such spray rails?
It seems that if they really work (the following reference claims they reduce the frictional resistance by ~12% at 20 knots based on tank testing of sailing cats: http://vm2330.sgvps.net/~syrftest/image ... 094246.pdf ) then the Supercat/ARC would benefit them most due to the hull shape.

Besides they look cool... :-)

Best Regards,

Alex

Mac M
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Joined: June 13th, 2012, 2:05 am
Boat Make/Model: SC20 & 17
Location: Lugoff, SC

Re: RE: Spray rails on Supercat 17

Post by Mac M » October 11th, 2017, 2:05 am

Seems like more trouble than it's worth to me.

Self tacking jib is a great upgrade to a 17 and definitely easier than modifying the hull shape. Spinnakers are fun too!

Matt Haberman
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Re: RE: Spray rails on Supercat 17

Post by Matt Haberman » October 11th, 2017, 9:45 am

I have not had a chance to read the entire publication but I don't think I would waste my time doing it.
A couple of things to consider:
  • It appears that all of the gains they talk about are around the 20-23 knot range. Pretty unlikely you will ever see 20 knots on 17 and even if you did it would only be for a very short period of time. So the question is what type of gains do you see at more typical boat speeds? My guess is that it is minimal at best.
  • All of this is based on tank tests which probably don't represent the typical sea state that you will be sailing in. I would suspect that most gains are lost in a typical sea state....
Matt Haberman
Aquarius Sail Inc.
http://www.aquarius-sail.com

Bill Roberts
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Location: Stuart, Florida

Re: RE: Spray rails on Supercat 17

Post by Bill Roberts » October 19th, 2017, 6:36 am

Alex,
Your first problem is the bulkheads showing through the hull skin. I think the hull vent holes in your boat are clogged. On all beach cat hulls there must be a vent hole to equalize the the pressure inside to outside the hull. Otherwise on a cold day your hull will show the bulkheads like ribs on a starving horse. On a hot day the hulls will blow up like the Goodyear blimp.

Spray rails: There are many technical reasons as to why spray rails do not work to a speed advantage in real life sailing on real water at 20 knots or 10 knots or 5 knots. Real life experience: The Shark class, 1960, came out with spray rails near the bow. This made the spray field wider and larger and it blew back on the sailors. Many sailors took the spray rails off and the boats went slightly on windy days.
In the Tornado class, 1965, some sailors added spray rails near the bow of their boats. The boats went slower. Today you see no spray rails on Tornadoes. Spray rails also increase the boats tendency to pitchpole the boat once they are pushed underwater.

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