Alright you DE guru's explain this

jerseysportfisher

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I swear the boat is a 31JC in the yard i'm in, the strange part about it it has a series of 3 steps on the bow, under the water line, each step is roughly 4 inches wide, an inch tall at the back, and about 3 feet long, they are setup vertically about 4 inches apart from each other, and almost look like gills. What is the purpose of theese ? I understand the purpose of steps in a planing hull, and how they really become efficient above 26 knts. No way in hell this JC is going 26 knots +
 

jerseysportfisher

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Strakes ???


There vertical not horizontal, i won't be down there today, i'll get pics tomorrow


like i said they look like gills


shark_giles.JPG
 

cb34

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steps

Must be to create air flow, same principle as steps on planning hull? My boat always ran easyer in a chop than it did flat seas for the same reason.
 

Tuna Pursuit

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the 31 JCs tend to steer by the bow in a following sea due to the razor sharp entry. That's why they are great in a head sea. My guess would be it's an attempt to give the bow more lift so it doesn't dig in a following as much.
 

steveinak

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Try talking with the owner of the boat, maybe it was a totally worthless addition. Might be something like a bubalous bow and breaks up the water to make it slide easier through the water ??
 

Badlatitude

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Considering he painted his prop I wouldnt assume there is a logical reason for the gills. If there was they would be on boats all over the place.
 

F/V First Team

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Might be to get up onto plane easier, I'd be surprised if they worked though.

If there is a lot of stuff in the forward section the vessel might have a hard time getting up and going. Even an inch down at the bow takes a tremendous amount of power to get it up (please, no viagra jokes here). If they did indeed put these up on the bow to introduce some air and break the suction of the water, that same air pocket would have given it less buoyancy at the bow because of the very same air they introduced.

We've seen something similar out on the races, someone pumping pressurized air in under the boat to reduce wetted surface and friction from the water by letting the boat "ride on air". Which is all said and good, however you need the water to support your boat, otherwise it won't go.

Their experiment halted soon after they were beaten on the course, I wonder why that was...

Another use of compressed air, which has nothing to do with this at all, is pumping it down into your shaft log from a scuba tank. This allows your propeller to cavitate massively to act like a trolling valve or more appropriately a transbrake whereas the engine can be at full rpm and over the turbo lag that is associated with over-propping and a turbo that is way too big. Shut off the air and you're already spooled up and away you go.

I hear it is quite noisy.
 

jerseysportfisher

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We've seen something similar out on the races, someone pumping pressurized air in under the boat to reduce wetted surface and friction from the water by letting the boat "ride on air". Which is all said and good, however you need the water to support your boat, otherwise it won't go.

The only sucsessfull hull that i know of used vents, with glassed tubes running into the steps was the rybo runner, and it worked, however with any stepped hull it usually doesnt make a difference untill the higher speeds. I have seen one stepped displacement hull from way back in the early 20s, the step created more of a pressure variance, where the water close to the hull (boundry layer) went undisturbed, and created less frictional loss on the hull. i can't see how what i posted works in any
 
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