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Hey everyone, I came across some photos of my friends modifications to the15 hull. On this occasion he just extended the strakes to the transom. This time he ground down to the glass, and created a dam to form the hull mod. The last photo shows how much higher the hull rides out of the water with the mods. Food for thought, this is the fourth hull he's done this modification to. Ask any questions.

https://www.dropbox.com/s/fvolcxb86t9...M.jpg?dl=0
https://www.dropbox.com/s/ajmlazyfbn4...M.jpg?dl=0
https://www.dropbox.com/s/sufg4rsw9wi...M.jpg?dl=0
https://www.dropbox.com/s/c4iyye9x6te...M.jpg?dl=0
https://www.dropbox.com/s/vwwq3kxk7nr...M.jpg?dl=0
https://www.dropbox.com/s/s1xyd45bzk9...M.jpg?dl=0
https://www.dropbox.com/s/et8sodijzzh...M.jpg?dl=0
https://www.dropbox.com/s/1sj9wptp5er...M.jpg?dl=0

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Running Photo and video

https://www.dropbox.com/s/ejw0fwl52ge...M.jpg?dl=0

http://youtu.be/B4e8kwmlUxQ

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Cool idea.
Is it harder to turn?
TP

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Not at all, we stole the idea from my Wahoo! 1750 CC Hull. I have owned the Wahoo! since 1995, and just was always astonished of how well the boat rode, and took waves. It was always faster than comparable hulls with similar power. I once spoke to a factory engineer, who said the boat was designed to ride on air, and the hull broke loose from the outer sponsons at 28 mph and just rode on the lower hull and strakes. The Whaler now behaves similarly with a nice flat ride, high out of the water. We have these hulls rock solid stable beyond 60 mph like this. But the real benefit was all around efficiency of the hull.

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That's funny,
when I was fixing our 1970 17' bottom,
there was a story of a black 15',
that had extended strakes.
Beautiful whaler, that happens to be yours!
(...spied your personal page)

Kinda wish I'd experimented with the mod
while it was upside-down.
The pangas have that "delta pad" flat spot on the stern,
and they're known for low hp efficiency.
The 17' whalers are the exact opposite in design,
more like a cut down canoe in the rear center section.
I wonder why?
It seems obvious that a rear flat planing surface would be a good thing.

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.

The early 17's have two pairs of strakes that look like they could be extended.
The 15' hull already has the outer runners shaped all the way to the back,
where the 17's are snubbed almost 4' short.
I'll have to research if later smirked 17's were extended or shortened.

Anyway thanks for the hot rodding lesson!

TP

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Hope all 4 hulls were not mischief's. No offense, I know your boat started life as a mischief too, but it seems like such a shame with their exceptionally low production numbers, to modify one or turn it into a "Sport" model. It is arguably one of the rarest whalers ever built. I have a friend who has one of 23 white mischiefs ever produced and he has been offered $20K for it with the original 70 HP Johnson on the back.

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Three were sports, only one mischief. All boats were done with gelcoat. I only own the black one.
One thing we figured out was the instability of the 15 hull was caused by airflow under the hull. This little mod fixed it.

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I think your black one is a very, "sharp" looking boat and the work is absolutely beautiful. Keep that Mischief, "top" as someday I think they will bring even bigger money as the Baby Boomers all go in search of their, "lost youth".

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I only ever had the black one, Eric, my friend, owns a company in Seminole, FL, he does the actual work. I just got to dream and draw. The mischief is his, but he ended up selling it to an admirer in NY State. The deck you are referring to was impossible to remold the non-skid, he tried. Finally he just sanded it off and put that padded material on it. This mischief was done impeccable. But most super nastalgic whaler fans find modding the boats a cardinal sin. I originally did a little 9' tender, restored to perfection. With the 15 (black one) I was chasing my youth. I built that boat for my older boys. They love it. Originally, I planned the black boat to be a perfect restoration, but later decided that he needed a boat to sort of kick start his business, which it did. I just got the benefit of owning it.

In regard to the quality of this restore, IMO this is easily the nicest mischief on earth.
https://www.dropbox.com/s/1sj9wptp5er...M.jpg?dl=0

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James, your black one also has a pad, in addition to the strake extensions, does it not? After seeing it with and without, is the pad needed?

Tim

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The pad, is only a must, if your goal is top speed. When my (black) boat is running at top speed, it's only running on about 3 square feet of hull, the boat "airs" above 55 mph. It's truly fun. The pad isn't a necessary mod. Extending the strakes have an overall benefit, imagine that it's like putting trim tabs on the boat. I've noticed benefits at all planing speeds. If you look at the standard 15 hull with no mods, running, the shape of the hull in the water is a cylindrical wedge. Extending the strakes gives the wedge shape running/planing edges. The pad we created for the black boat, lifts the hull another 6" out of the water at high speed. If you estimate the running surface area and drag associated with the three design mods, the original ran on about 12 SF, the strake mod reduced that to around 6 sf, and the pad further decreased it to 3 sf. Essentially it's many times less drag. My engineer could figure it out, but I have no idea. I also saw this done on another 15 in SC that was dark blue. After I read his story and saw his pictures of mods, he was definitely on the same path we took, but the pad designs were pretty different. His pad was a bump, and if the boats bow would bounce, the leading edge of the pad had the chance to dive into the water. I'll post some pad pics if I can find some.
http://i1320.photobucket.com/albums/u...3b07a9.jpg
http://i1320.photobucket.com/albums/u...dd078c.jpg

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Best one I could find

http://i1320.photobucket.com/albums/u...315506.jpg

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Thanks James! I appreciate the input. I'd love to extend the strakes on my 15 at some point. The design of the aft part of the stock 15 hull makes no sense - loses all lateral stability once you get the strakes out of the water.

Tim

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Thanks James! I appreciate the input. I'd love to extend the strakes on my 15 at some point. The design of the back part of the stock 15 hull makes no sense - loses all lateral stability once you get the strakes out of the water.

Tim

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Me too!
TP

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Apparently I felt twice as strong about it. Oops.

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No worries, if you need measurements just let me know. Sometimes we joke, without the mods, going fast in these is like doing it in a snow saucer. Fun but stressful. I'm always available if you need any info. -JT

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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.

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Tim, the 15 as you know, starts to wobble and chine walk, because the angle of the bow is trapping too much air for the hull to release at the stern predictably. Extending the strakes, lifts the stern and provides a regular exit for the air pressure under the hull. Lifting the stern at speed, also lowers the bow, and less air going under the hull. The little pad on the bottom of the black boat furthers this. I do believe, that my black boats stablility is enhanced because of the high performance hydraulic steering. I've had the UFLEX SilverSteer system, from the get-go, so I'm not sure of a comparative benefit of not having it.

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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.

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

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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.

Anyway just thinking out loud...

TP

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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.

If you do it the way we did the black one yes, if you add a padded keel feature, no.

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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.

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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

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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.

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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)?