cavitation height

[David CVX-16]

A proven route with a jackplate is to buy a factory boat and motor where the manufactor with their resources has done the hours of testing with various setbacks, motor heights, and prop combinations to maximize speed with the setup. 

An example is Bullet bass boats. You can buy them prerigged from the factory to go 100 MPH+ with a 300 HP Mercury.

 

[WetRaider]

It looks to me that some of those fishing boats are using the set back distance to create deck space for stepping around while reeling in the catch of the day - no splash well to slip into inadvertently, or any cabling to trip on. 

For boats that are rated with a motor mounted on the transom, a set back would create additional stress, as the mounting bolts turn into a fulcrum point with the weight distributed further away (generates a moment force), like adding an extension to your socket wrench.

[terry]

Greg yes its a 20 foot vt rocket.has hydraulic steering and a tunnel haul.there is not that much I can find on the boat or any past articles.some guys over on scream and fly have them.they say they dont like to turn that well they want to hook in corners.the guy who owned it before me ran a evinrude 225ho and gps at 86mpr with a 24 tempest.im guessing with the 200 mariner would be upper 60s maybe low 70s.your only talking 25 hp.but I think the 225 was more like 250? With the ho and fuel injection.

[Hyperacme]

Can't find a good picture of your stern ...
But Hydrostream made some hull designs that look pretty close to yours.
Is it close to the VT, XT hull's in picture ?

YA !  ... Cool boat Terry !

[terry]

Kinda like a vallero yt but I think I have a deeper tunnel.I'll post a picture when I get home.I know when you look at it from the bow under you can see clear to the back.I would say looking at diagram would go with the at design.

[Oldfishguy]

I know speed is important, but so is manurerabiity at speed.  Our boats lean in the corners and we all know you have to keep that prop buried in the water for tight control.  The height of the prop is always a compromise; depending on what your hunting for.

https://m.youtube.com/watch?feature=youtu.be&v=kpCSUROVxwE

[OleRed]

yep, speed is good, and so is handling, but you can have both with the drive raised 3" and set back 6" ... and the right prop, the first turn was probably mid 30's, I think we were doing 65 or better  around the bend in the river, trimmed up it was mid 70's with 5 of us on board, Chris had his gps.
https://www.youtube.com/watch?v=3T3YVy2kEow

Second video just one of my favorites
https://www.youtube.com/watch?v=I-kK0gSKHlo

But ... a turning hole shot will blow a the 27 pitch powertech, I came into the cove @ 55 / 58 mph before opening the throttle, that motor and prop ran a 78.2 by the gps
https://www.youtube.com/watch?v=0_MQOnVzH6U

I do miss that boat   

[Hyperacme]

"I think we were doing 65 or better  around the bend in the river, trimmed up it was mid 70's with 5 of us on board, Chris had his gps."

That was the ride of my life Red !

[Oldfishguy]

yep, speed is good, and so is handling, but you can have both with the drive raised 3" and set back 6" ... and the right prop, the first turn was probably mid 30's, I think we were doing 65 or better  around the bend in the river, trimmed up it was mid 70's with 5 of us on board, Chris had his gps.
https://www.youtube.com/watch?v=3T3YVy2kEow

Second video just one of my favorites
https://www.youtube.com/watch?v=I-kK0gSKHlo

But ... a turning hole shot will blow a the 27 pitch powertech, I came into the cove @ 55 / 58 mph before opening the throttle, that motor and prop ran a 78.2 by the gps
https://www.youtube.com/watch?v=0_MQOnVzH6U

I do miss that boat   

Nice!

That is a well balanced machine.  Hull, engine, prop, and it looks all proportionally like it fits together perfect and handles like we would hope.  That doesn't happen by accident.

[Hyperacme]

Hull Technology in Hydrostream boats ...

http://www.hydrostream.org/ArticleArchives/HullTech.htm

[David CVX-16]

Very good article Gregg. Alot to think about when trying to get into the 60 to 80 MPH range.

 

[Hyperacme]

More info on Strato VT ...

http://www.screamandfly.com/showthread.php?180947-Stratos-VT-ROCKET-VT180-1986

[V153]

Ehh ... I say speed trumps handling ...