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Then there are the early 13's,
which have two long skegs in the rear.
Those things turn on a dime,
and track like a longer boat on fast wide arcs.
TP
TP, I never really understood the design of the 13, I've seen so many upside down. I truly believe the design was for floating stability. I see a bit of "sea-sled" inspiration for the design in the front of the hull pre smirk. When I was growing up, my neighbor friends had a 13 with a 40, and they used to take neighborhood kids on rides just to throw them out of the boats by turning hard at high speed. I was a victim of the prank.
This may sound like whaler heresy,
although I really hold the 13' in high regard.
When you said you never understood the design,
it made me remember a couple moments on the creeper,
when doing some ding repairs.
Nothing really flows on that whaler bottom,
there are so many permanent modifications to the design.
I was imagining them starting with a smoother prototype,
and experimenting to fix its faults,
adding the double side chine to fix spray,
the harder rails/strakes for tracking,
and the skegs for slipping...
What did they try that didn't work?
It makes me wonder how much the 17 and 15 hulls
changed from prototype to finish.
What was the reasoning to shorten the strakes (and side chines on the 17)?
Definitely a learning period of cathedral hulls.
tedious wrote:
James, I was thinking of it more simplistically - once you get going fast enough so the strakes are out of the water, you're running only on the rounded portion of the hull, which is a section of a circle, so the boat can roll from one side to the other with no resistance. I am sure the air is a factor too, especially for boats with extra horses on the transom.
You are right, but the bows angle of attack into the air, creates the amount of air captured under the hull, and your Cg has a lot to do with this too. Once the hull starts to roll on its keel the air pressure starts to spike on one side (as the other releases) causing the chine walk. When the boat is going fast say, near 50 mph, the Cd in the water vs the Cd of the hull in the air ratio gets much closer percentage wise. Most people discount the effect of air on a high speed object simply because its invisible. The only two types of vehicles that don't have to deal with dual coefficient of drag are submarines and aircraft. Everything else must. A great example of this is my old 2009 Fountain CC, I had a 34' with triple 300 Verados. When I was researching the purchase from comparable brands, nobody's offering could touch the performance of the Fountain with the exact same power. The weights, lengths and power were all similar, however the Fountain hull was significantly more efficient in the water because of two features: 1. was the true stepped and ventilated hull. The design drew air under the hull to change the Cd of the lower running surface. 2. The padded keel, essentially a vertical pad the extends from the hull down about 1.5" and is 12" wide. When the boat is on plane and running you will see the strakes, because it lifts the boat so high out of the water. I can attest that in completely calm water, it would rock side to side with a little wind, but it never changed course. Fountain knew their stuff, the still hold the mono-hull speed records. When other triple engine boats were running mid to high 60's, mine ran 80.
tedious wrote:I wonder if stock power can push the hull fast enough to make the "pad" worthwhile, or if the extended strakes would be sufficient.
Tim
If you do it the way we did the black one yes, if you add a padded keel feature, no.
Perichbrothers wrote:
[quote]jamesgt727 wrote:
[quote]T
What did they try that didn't work?
TP
They should have at least added a little hook into the hull at the transom between the skegs to control the porpoising....And maybe a little vent feature the smirk out the side under the forward sponsons! The 13 i spoke about above porpoised so bad it was crazy.
jamesgt727 wrote:
If you do it the way we did the black one yes, if you add a padded keel feature, no.
That makes sense. Do you know if any of the other boats that were modified like the black one are running with 70s? I am wondering what performance differences were seen.
Tim, no. But the other two Eric built, had New Yamaha F70's, and the strakes extended. I never got a chance to ride in them before they were delivered to the owners. I'm really surprised they didn't show up on this website. It's a shame, they are really nice and very interesting. I did hear the F70 was a great motor combo.
I know I am resurrecting an old thread. I’m wondering if anyone has any performance data on a Classic 15’ with the strakes extended and running rated horsepower (70 hp)?
