What is the maximum deadrise angle?

[jfblouin]

I would like your opinion about what is the maximum (and raisonnable) deadrise angle for a deep V planning hull, at transom, midship anf aft?

[fede]

As I know there is no "Maximum" ,however there is what is commonly used,and I have seen anything ranging from 15 (workboats) to 30 ° (fast offshores).
It depends on many factors, kind of waters you are going to use the boat (lake,river,sea), keep in mind that the more "deadrised" a boat is the better it will keep the sea, but the more problems you will have to solve as far as performance is concerned,deadrise has been introduced to cut waves,falt bottom is perfect (except when turning) when you have perfectly flat sea,but when you have rough sea you need the V not to BUMP too hard from wave to wave as the V cuts the wave making the ride smoother,the more the V the smoother the ride,the less the hydrodinamic lift.
As often in boat design it is a matter of compromise.
I've seen that a deadrise of around 22 24 (always speaking of transom) is what I see is more used, in my believs V at the transom should be rounded off (speaking of fast powercrafts) to have a better lift,I've seen this done on a couple of crafts and it works.

As you move towards stem, again...I've seen up to 60° (!) on some offshore oriented crafts, 40...50...there si no rule.



Remember that deadrise from midship to stem affects interior layout a lot, if you keep a very high deadrise, you might have perfect performance at 80 knots but no space.

You can 't simply have a high dedarise forward if they asked you to draw a 40 feet boat with 3 cabins!!

Also you can't simply have a 35 ° deadrise forward if they asked you to design a 90 mph monster

I usually decide transom deadrise and then let the design guide my decisions.



As always, this is just my opinion, I might be very wrong!

[jfblouin]

I want to build a boat whit this specs: max speed min 50 kmh, cruising speed 30 kmh, 7m lenght and 2,60m beam (trailerable).

I will use the boat on open sea whit 1m - 2m waves. the boat will be a kind of RIB but whit hard boyancy tubes.

My first plan have 30 deg transom and 45 deg aft deadrise angle but I want to be sure that this boat will be navigable.

[fede]

the relative speed of your boat is 5 (v/sqrt L)
for that relative speed i think a deadrise of 21.5 22 is fine.
speaking of midship and frwrd perp. oyu might go with something around 27 (mid) and 35 (up to 40) (frwrd perp.)

As always...I might be wrong...(hope not!)