Adding a "pocket" to a transom?

[wanagofass]

I've got an early 70s v-bottom w/no pad. The transom is flush with the keel and it likes some setback to carry the bow at top end, the problem with that is how it sits bow high at rest with the setback. I've been toying with the idea of adding a pocket to the transom to help carry the bow at speed but not cause it to sit so bow high at rest. Just wondering if anyone has done it or really knows boat design who can tell me what side effect it may have, or Howe to shape it/how wide it should be.

[XstreamVking]

When you take away hull volume from the stern (make a pocket shape) it will sit lower in the water, and be more nose high than it is now. The intention of the pocket is to add "built in" set back to the hull, and get water to the prop when planing off with elevated engine heights.

[W2F a V-King]

What propeller are you running now and how high?

There are propellers designed for bow lift.

[wanagofass]

I know a pocket/notch will decrease displacement and cause the boat to float more bow high, but I wouldn't think it would be as bad as adding setback to the jack plate.

[wanagofass]

The fastest setup so far was 4" setback, and prop shaft about even with the bottom. Offshore cut chopper.

[XstreamVking]

There is a formula for how much weight each cubic inch of displacement supports.

[tunnels]

i know a pocket/notch will decrease displacement and cause the boat to float more bow high, but i wouldn't think it would be as bad as adding setback to the jack plate.

add all those things added together and you get what you got !! Theres more than first meet the eye doing modifications and chopping bits off and exstending motors etc etc what ever you do changes other things ! So you need to be sure the gains at hi speed you looking for are well thought out because there are down sides to each mod you make !

[tunnels]

The fastest setup so far was 4" setback, and prop shaft about even with the bottom. Offshore cut chopper.

When you dealing with performance modifications there is no such word as ABOUT !!it either level or there's a measurement up or down never ABOUT !!

Set back also changes your feel of the steering also !! I had 450mm set back from the end of the transom and the tracking in rough ocean swells was excellent But was able to turn in a tighter circle so became more manoeuvrable ! The outboards power trim also was much more positive and way easier to fine trim and I learned very quickly how to find the sweet spot all boats have looking the rev counter and using the trim button plus reading where the spray was coming out the side of the chine !!

[tunnels]

There is a formula for how much weight each cubic inch of displacement supports.

just posted "DISPLACEMENT" formula in real simple term's

[MattGreen]

I'm considering doing the same thing to my Scarab 21, which has a pad but no pocket/notch. There are some threads on here about SOBs where this has come up, with good advice and pictures. Post up what you find out. Also try to measure or at least take pics of similar sized boats to get ideas. Fountains for example have notches and had engineering departments and lots of test time, perhaps a decent place to start in the absence of other info.

Matt

[tunnels]

I'm considering doing the same thing to my Scarab 21, which has a pad but no pocket/notch. There are some threads on here about SOBs where this has come up, with good advice and pictures. Post up what you find out. Also try to measure or at least take pics of similar sized boats to get ideas. Fountains for example have notches and had engineering departments and lots of test time, perhaps a decent place to start in the absence of other info.

Matt

My first questions are why do you want a pocket in the transom ?? what do you really hope to accomplish and gain from it ??

In a small way I have played with the pocket concept and its issues and I feel there are only small advantages but be very careful as with all things there are down sides as well .Loss of buoyancy and if the shape is wrong suction in the early stages of taking off and momentary lowering the back but all this is to do with shape !!
Look and find as many pictures as you can find and all the info anyone can tell you .
I solved my issues that id experienced by changing the transom completely on some small boats I was manufacturing plus on my own small fast fishing boat I designed and rebuilt a complete new fibreglass transom that was just 1/3 if the weight and incorporated shape and set back and raised the motor height to take a 25 inch shaft !! I intergraded two problems together and came up with one single solution !!

[vnemous]

I'm considering doing the same thing to my Scarab 21, which has a pad but no pocket/notch. There are some threads on here about SOBs where this has come up, with good advice and pictures. Post up what you find out. Also try to measure or at least take pics of similar sized boats to get ideas. Fountains for example have notches and had engineering departments and lots of test time, perhaps a decent place to start in the absence of other info.

Matt

Matt is your Scarab an outboard? If its an I/O you obviously will not be able to raise the motor and will actually slow your hull down. As far as suction on take off from a "notch" all you have to do is vent it and you will not notice any suction. Much like Fountain does and I had to do with my 21 Super Boat after it had been notched.

[MattGreen]

Matt is your Scarab an outboard? If its an I/O you obviously will not be able to raise the motor and will actually slow your hull down. As far as suction on take off from a "notch" all you have to do is vent it and you will not notice any suction. Much like Fountain does and I had to do with my 21 Super Boat after it had been notched.

Hey, thanks for the advice, it was exactly the NJ/NY SOB boys I was thinking of when I posted that. I think lots of guys in your area have had notches added right ?

Yes, my Scarab 1 is an original factory OB boat. It's a lot slower and heavier than a Suoerbiat/Challenger type of hull. Do you have any pics of the notch and vent setup ? I think Tuff ventilates them too.

Matt