General shape / class of the jet boat hull bottom ?

[cyclops2]

Warped bottom
Modified V
Deep V modern 19' bow riders
full length constant deadrise V

Assuming a boat about 20' & V8

[baeckmo]

Generally speaking: constant V preferred over warped, because thrust line of jet is higher than tl for a prop installation, which increases bow-down attitude. Minimum bottom angle ~10 deg helps in keeping intake free from bubbles generated at spray-root forward.

Double chine hulls work excellent with jets, giving low resistance and soft ride. Remember NO DISTURBANCES in front of intake and within minimum 150% of intake width!

[cyclops2]

Where can I find some hull photographs or manufacturers that make very good hull designs ?

[speedboats]

Originally Posted by baeckmo

Generally speaking: constant V preferred over warped.... NO DISTURBANCES in front of intake and within minimum 150% of intake width!

Not always, there are ways around it...

At 19' to 20' some of the big boat rules can be bent. Jetsprint boats run a transom deadrise angle up around 24*, I've used 19* extremely successfully with a warped bottom.

What sort of vessel are you looking into? River, cabin, sea-going?

[Eric Sponberg]

Originally Posted by cyclops2

Warped bottom
Modified V
Deep V modern 19' bow riders
full length constant deadrise V

Assuming a boat about 20' & V8

The attached perspective drawing shows you what I did on the Cherubini 20 bottom for the jet drive. The deadrise for the aft half of the hull is constant at 20 degrees, but there is a slight rocker to the keel line--it is not straight. The bow sections a convex and have higher deadrise. So, you might say that this is a combination of all of the types you list above. This shape was sized for the Mercury jet pump. It runs extremely well.

You can see some photos and drawings on my website:
http://sponbergyachtdesign.com/CC20.htm

You can see Cherubini's website here:
http://www.cherubiniyachts.com/20.html

I have used a similar bottom for the Saetta 20, which originally had an inboard drive, and I have just reshaped the hull for a jet drive using a Hamilton jet. That is being set up as a kit now. You can see the Saetta 20 here on my website:
http://sponbergyachtdesign.com/Saetta.htm

And here at the Saetta website:
http://www.saettaboats.com/

I hope that helps.

Eric

[cyclops2]

Guess it is time to show the woodie that needs a below the waterline, NON HOOKING, cleaver / vertical bow. Rouge River jet boats told me that my gut feeling of using a ..constant deadrise all the way to the transome is ONLY used in their rough river water boat. My logic of constant dead rise & vertical bow creates a non visable keel. that provides the extreme straight ahead in the worst chop & waves......Speed & efficiency mean nothing in this boat. A 5 L 220 hp inboard should easily give 40 to 45 mph. Perfect.

It will be built as a rear 2 person, Gentle Man racer. I have cut up the full depth keel, engine stringers 23 degree triangular bottom frames. Frames are every 12" to prevent twisting of the hull. I will use the 1/2 way notched & interlocking assembly of the deep V bottom. Plywood for strength & a probable wood hull not to exceed 500 pounds.

The boat will hopefully go THRU a wave of any height. Rather than be tossed 6 feet high. Have done that in my 19' V8 Chaparral. Teeth stopped 2" from the Aluminum windshield.

Boat should not bow hook or become airborne unless I am stupid or showing off like a nut in a 21' X 4' boat.

Rich

[cyclops2]

Obviously ALL interlocking joint will have FULL LENGTH triangular 1" x 1" soft Pine gusset blocks to lock the weakned joint securely. The same gusset blocks will be used on both sides of anything holding the marine plywood skins on. A final vacuum bagging of veneers will cover any plywood appearence.

Plywood for twisting & pounding strength. Veneer for appearence.

Rich