Dead rise and nothing to do with Hammer House ...

The Jackeens · 30 March 2004, 17:23

So you techo bods out there can you explain in short, easy terms, what deadrise means.

Chow

Paul

Dirk Diggler · 30 March 2004, 18:01

It's the V of your hull, (angled bit between chine and keel).

The Jackeens · 30 March 2004, 18:13

Thanks Mr D,

why can't they all say V and not deadrise.

I don't know boat builders

Paul

John Kennett · 30 March 2004, 18:27

It's this angle:

robin · 30 March 2004, 18:35

Definitely not this one then?

robin · 30 March 2004, 18:40

I have just looked at that picture again. Engine could do with trimming in a touch. Fnarr

The Jackeens · 30 March 2004, 19:29

Who's that then, have ya painted your red red then

Paul

steedthrust · 30 March 2004, 20:36

Then how does it then affect your boat?

Low deadrise faster I assume but less seaworthy?

Mines 24 degrees is that low/med/high?

Also i seem to have concave chines how does that affect the boat?

John Kennett · 30 March 2004, 21:17

Steedthrust

The shallower the V, the easier the boat is to get on the plane. It will need less power, but won't necessarily be faster as this will depend very much on the sea conditions.

The deeper the V the more the hull cuts through the waves giving a smoother ride. It requires more power to drive the boat though.

RIB hulls tend to be medium V (10-16 degrees-ish) or deep V (around 16-24 degrees-ish).

Medium V hulls give a generally good performance with modest size engines, but will be hard work when the sea is choppy. You wil tend to find these at the smaller end of the leisure market.

Deep V hulls are more suited to offshore use, but tend to need bigger engines and are less economical to run.

This is a gross simplification of course as there are all sorts of variations, such as variable deadrise hulls and planing pads to take into account.

Concave chines will add lift, but tend to make the ride harder.

Planing hull design is a remarkably complicated art, and although it may seem that different designs are similar there are often considerable differences. On the other hand there are also occasion when they are a direct copy of something else . . .

John

PS Robin, no not that angle!

Colin F · 30 March 2004, 21:26

anything over 18 degrees is considered a deep V ie your at 24 degrees, this cuts through waves, rather than slamming over them. this means deep v hulled boats are more comfortable in choppy / rough conditions. anything less is considered a medium V, generally down to 12 degrees, below that it is unlikely to be found on ribs intended for sea use.

while i was checking my info (it is over 6yrs since i studied boat design - grey cells diminishing) i also found this website that gives some info on boat design aspects- beware though its yankee doodle, so some terminology could be different.

http://www.marathonmarine.com/Boat%2...m#_Toc38684154

boats can be constant deadrise ie. the same angle all along the hull, or variable / progressive deadrise in which case the deadrise increases towards the bow.

Colin F · 30 March 2004, 21:30

jk - too quick typing for me!!!!!!!!!!!!!!

ps i always find terms deep/medium v a bit vague and generally ask for the exact angle - then you're in no doubt

Colin F · 30 March 2004, 22:23

drawing below (if it attached ok) shows a section at the transom. the chine is typically a lot narrower at the bow, getting bigger towards the stern. This one is a slightly concave chine. spray rails also shown, these get water off the hull and away from the boat - less surface friction and a dry ride if it all works as planned!

I hope i've remembered this all ok, but i'm prepared to be shot down if not..........

robin · 31 March 2004, 06:39

Quote:

Originally posted by The Jackeens
Who's that then, have ya painted your red red then

Paul

Nice boat that, Osprey sparrowhawk, wobbles like a wobbly thing at rest (very deep v) but as smooth as silk in a sea. Not mine, is one used for training (on its last legs now sadly)

robin · 31 March 2004, 06:42

Quote:

Originally posted by John Kennett

PS Robin, no not that angle!

Ta for that. Someone once explained to me what deadrise was, i must have been very drunk at the time or just my usual hard of understanding.
What is that angle called?

Jon Brooks · 31 March 2004, 07:26

Quote:

Originally posted by robin
Nice boat that, Osprey sparrowhawk, wobbles like a wobbly thing at rest (very deep v) but as smooth as silk in a sea. Not mine, is one used for training (on its last legs now sadly)

Where is that one based?
Looks very much like one of the boats I used last week on my Safety Boat Course.

Oh I passed by the way!!

Regards

Mark Halliday · 31 March 2004, 09:28

Is that the flat bit ahead of the prop? All sorts of odd shapes under here. Dead rise seems to be 24-25º. Very different at the chine which ends 3" foreward of the transom.

Mark Halliday · 31 March 2004, 09:30

Have a look at the angle of the front and rear rollers.

P.S. Rusty bits to be sorted over easter.

Headhunter · 31 March 2004, 09:59

Mark

Your rear rollers are further outboard than the front rollers so the angle will be different.

The hull seems to flair outwards all along as it reaches the tubes.

John

robin · 31 March 2004, 10:01

Quote:

Originally posted by Jon Brooks
Where is that one based?
Looks very much like one of the boats I used last week on my Safety Boat Course.

Oh I passed by the way!!

Regards

It is one and the same. Mark said you had passed. Well done.
I was meant to be there to assist him but I couldn't make it.

Jon Brooks · 31 March 2004, 10:05

Quote:

Originally posted by robin
It is one and the same. Mark said you had passed. Well done.
I was meant to be there to assist him but I couldn't make it.

Oh your that Robin

Was a good course, learnt a lot.
Just need to get more time on the water now.

Regards