Hull blue printing

[anthony_marquart]

The bottom of my UL-19 hull was a little wavy. I’ve block sanded it down to 220. How fine should I go with the grit? Thanks.

 

[Mike Cathey]

If you are planning on painting it I would finish sanding with 150 grit before primer, so the primer has something to grip to. You will also plainly see any pinholes or other blemishes that might need filling and sanding as well. Sand the primer with 220 grit before the color coat.

I have seen a couple of guys use too fine a sandpaper for final sanding and the paint job coming off in big sheets. They were CA'ing the paint job back on during the race.

 

[Timbo Whalen]

800-1000 final finish for least hydrodynamic resistance.... block sand perpendicular to the boats direction of travel on

the running surfaces.

Hope this helps.

 

[anthony_marquart]

Thanks guys

 

[John Beardslee]

800-1000 final finish for least hydrodynamic resistance.... block sand perpendicular to the boats direction of travel on

the running surfaces.

Hope this helps.

Tim
Where did you get those grit numbers for least resistance? When I visited a friend of mine at the propulsion engineering division of Mercury the grit number was 400. It was many years ago so maybe it’s changed but that’s what I’ve always used.
Thanks John

 

[anthony_marquart]

Well. I sanded to 800. It’s much “slicker” than it was. Can’t wait for new motor and esc to arrive. I have a couple props I did and a couple from mark. I have added extra cooling, the Mojo turn fin. Slightly bigger leapard motor and 180 amp esc. I just want it to as fast as the last sport 20 I built. (Which was fast for a sport20!)

 

[anthony_marquart]

Well. I sanded to 800. It’s much “slicker” than it was. Can’t wait for new motor and esc to arrive. I have a couple props I did and a couple from mark. I have added extra cooling, the Mojo turn fin. Slightly bigger leapard motor and 180 amp esc. I just want it to as fast as the last sport 20 I built. (Which was fast for a sport20!)

Now I need to upgrade this junky transmitter!

 

[Timbo Whalen]

Tim
Where did you get those grit numbers for least resistance? When I visited a friend of mine at the propulsion engineering division of Mercury the grit number was 400. It was many years ago so maybe it’s changed but that’s what I’ve always used.
Thanks John

John, just from experience...I should have mentioned also that, again from experience, hull type and how much it displaces, along with shear velocity, is technically relative.

3M, years back, made a mylar applique that mimicked the surface of shark skin. The project was funded by the sailing syndicate that supported the American team.
We contacted 3M in an attempt to get a sample, but it appeared no one knew anything about it.

My question is, did your friend have anything to do with the intricacies involving rc boats?...

On an outrigger hydro, or any hull where additional AoA is relevant, too course of an approach will actually induce drag.

My present hydros seemed to run wetter with 400 grit finish...key word 'seemed', as high speed video wasn't used for validation. We just upped the grit until the boat 'felt' right....also, I think there's a difference between what we did to front sponsons and rear shoes. Of note, we also coated running surfaces with graphite impregnated 207, all Gougeon Bros. West Systems products.

In finality, I guess to each their own.

 

[John Beardslee]

My friend was the propeller propulsion engineer at Kiekhaefer in Fon de Lac, WI. It’s was many years ago and they were using what ever the latest testing process was at the time. He was an active outboard racer at the time and also worked with many racers for infield testing.
I was wondering with your background you may have run across a study that identifies a better process.
Thanks John

 

[Timbo Whalen]

My friend was the propeller propulsion engineer at Kiekhaefer in Fon de Lac, WI. It’s was many years ago and they were using what ever the latest testing process was at the time. He was an active outboard racer at the time and also worked with many racers for infield testing.
I was wondering with your background you may have run across a study that identifies a better process.
Thanks John

John, it could get quite involved for public forum.

But, yeah, I'd love to get together with you, hopefully next summer, and bench race this stuff... I'll send you a PM.

Thanks-

Tim