Hull speed improvement

Lets think here!

Anyone can do any type of testing they want. But the way you prove it is to do it. If winning races doesn't prove it! I'd like to know a better way to prove it! When we build boats and race them, that's just the way we prove if the hull design is the fastest. It's cool to do a test in a controled environment. Each of us in this world of boating have done alot of our own research. I respect everyone in here who gives their opinions. We all know we won't always agree, but we all strive for the same thing. MORE KNOWLEGDE! Best wishes to all in their work!

 

Sure, as long as you don't claim that it is in any way scientific.

You, and no doubt, several others do it that way. I would dispute your implication that all or even most builders and designers do it that way, however. There is no proof of that.

Sure, and controlled environment experiments are not always applicable to real "field conditions".

Of course. And some has scientific merit, and some doesn't.

Cheers,
Leo.

 

It worked only within a very very limited speed range and only when the stuiff was correctly aligned with local waterflow. Outside that speed range it was worse than useless. Fortunately 12m yachts only work within a very limited speed range.

 

Read Frank Betwaite's "HIgh Performance Sailing". He did sensitive two-boat tow tests to look at this issue. His conclusion is smoother is better.

Sailplane pilots not only look for a polished finish texture, they've learned to measure the waviness on scales between the finish texture and the overall fairness of the surface. With a simple wave gauge you can measure the waviness in the streamwise direction. Sailplane wings are not that different in size and Reynolds number from centerboards and keels. Waviness as little as 0.1 mm (0.003 in) can have a detrimental effect.

 

A surface with a roughnes of about .5% of the diameter of the curve in the leading edge produces small vortices that delay laminar separation. This is specially advantageous in foils, masts and other smaller apendages. As with hull speed, appendages, masts, etc. also have a "displacement speed". When a hull is at displacement speed the keel and rudder have surpassed it.

 

I am laughing at all the answers we have posted. Salmon release a super slippery slime as they build up speed to jump a waterfall. Sharks have sandpaper all over them to make a high speed attack.----It is so funny.

 

Paint ...

I'm going with the Bethwaite concept of "it can't be too smooth".

My boat is in the yard for a few months for winter storage and a refit. I'm taking the paint off the bottom down to the epoxy barrier that was done 20 years ago.

Once the paint is off, I'll survey the bottom and decide if the existing barrier coat can be left on the boat or if it should come off so I can start over. The boat has some small (thumbnail sized) blisters.

I want to get the hull dry before I renew or replace the barrier coat.

At that point I'll have my choice of finish.

Is there an anti-fouling paint that can be sanded to 1200 and or polished? I undestand the IACC guys use Awlgrip and dry-sail. Is there an anti-fouling that is as hard as Awlgrip? If not, I'll dry-sail the boat.

The rudder is new, so it doesn't need much as far as fairing goes. The keel is in need of work. I have not been able to find what section the keel was supposed to be, so I have freedom of choice there.

Mars can provide generic templates based on chord and thickness. Does anyone have experience with them? The other option would be to take lines off the existing keel and find a section that is a close fit and use that.

The boat is a Catalina 30, she is never going to be an upwind bandit, but fairing the hull and foils will give the old girl a chance to be as good as she can be.

Yes, I know that the expense of doing the bottom and keel will be a large percentage of the value of the boat and does not make economic sense. For the same $$$ I could sell the C30 and buy a higher performance boat. Befana has been my faithful partner for 11 years now and rather than divorce her for a younger woman, I'm sending her to spa so she'll feel like a teenager again.

 

Old wood is all heat and no smoke.

 

Hopefully, one day I'll sail so well, that I'll be able to notice the difference...

bye
Hans

 

She'll never feel like a teenager again. Too loose. Baltoplate and the VC paints are really hard, and almost as fast as straight gelcoat. I've heard of an awl-grip paint called awlstar, don't know much about it though. You'll probably be best off with baltoplate, wetsanding it, then burnishing it with bronze wool to give a really, really smooth bottom. Wipe clean once a week.

 

LOL! Too loose!

After looking at what I can legally use in Canada (Baltoplate is not available), VC Offshore seems to be the choice. We're not allowed to spray paint anti-fouling up here. I'm hoping I can get the finish right with a roller and tipping the finish.

It's odd, but dry storage is less per month than a slip. If I can get a contract with the yard for a 6-10 haul & block package deal it will be less expensive to dry sail than pay slip fees.

 

If you can't spray anti-fouling, and you're going to drysail it, you may be able to spray VC teflon (which I don't think counts as an antifouling). Use a thin foam roller, and you may be better off if you don't even tip (though you'll have to put more paint in every 2 ft). Just be prepared to wetsand.

 

Same in my area. I leave the 16' alum in winter storage. No trailer maint. or fees or insur., all adds up. Heck of a lot more fun too.