Deadrise, How important?

[Flex]

Hi all. Im feverishly researching all sorts of things in anticipation of buying myself a larger plate boat.

I've got a few options on the list new and second hand, but a decision thats killing me is hull design.

Im looking at a riptide with a 17 degree deadrise and a new fisher/bluewater with 21/23 degree.

How much of a difference in performance and fuel economy would these 2 hulls be? (all boats being around 6m). Would the difference be significant? or hardly noticeable? (disregard stability at rest).

[PinHead]

performane..the 23 should be better...deadrise is measured at the transom..the entry lines also have some effect on the handling of the boat.
fuel economy..I doubt you can compare boats in regards to fuel economy as weights, laods carried etc etc ..so many variable.
does actual fuel economy really enter into the choice of boat or is it more for the range required? If the latter, just get a bigger fuel tank fitted.

[BM]

Deeper the deadrise the better the ride. Although 2 boats of equal weight but differing deadrise will not necessarily mean the deeper vee hull will ride that much better.

Deep vee and extra weight will be a better riding hull.

23 degree deadrise would really want a hull weight around 1000kg. What do the boats you are considering weigh?

Cheers

[Flex]

Its more range. I am eventually planning to be able to the boat up past cooktown or 3-4 day extended trips on my days off as I do shift work. So having the ability to travel 200-300km round trip is needed+a bit extra. but performance in rough conditions would be paramount, as carrying more fuel wouldn't be that difficult and Im assuming boat weights are identical. I wouldn't imagine fuel consumption would be that significant between a 17 or 23 degree..but Im no expert.

The boats im considering are a 6m riptide loaded would weigh around 1 tonne.

Or a fisher/bluewater 6metery which would weight roughly the same.

[BM]

whats the bare hull weight though (without engine)

[nautilus]

General rules of thumb:

Deeper the deadrise (DTD), softer the ride
DTD, the less stable the boat will be at rest
DTD, the worse the fuel economy

If the deep v has wide chines, it should be ok at rest.

If you are considering travelling large distnaces and it is a plate boat, I suggest having an extra fuel tank built in, or carry the fuel. The differnence in fuel economy is unlikely to be huge, but a softer ride over long distances would win hands down for me every time.

I had a look at both websites and I think I would be leaning towards the Fisher.

Just my 2 cents

[Catlover]

More deadrise doesn't mean better ride in all conditions when it gets really rough some boats with too much deadrise flounder between planing and falling off the plane and also tend to broche in a following sea if you want the best of both worlds buy a cat

[Flex]

whats the bare hull weight though (without engine)

Bare Hull weight dry is 900kg,

[BM]

Should go well then. 200kg for the engine, another 200 or more for fuel and gear. So 1300kg+ and a 23 degree vee would be a good riding hull.

[Stuart]

Flex

Sites like this are great to get information from, but when it comes to this sort of question you rely should be consulting with a naval architect. You have asked a question that will get you a different answer for every post as can be seen here. When I was looking at plate alloy hulls I didn’t even bother asking questions here or on any site for that matter because everyone has different opinions and ideas on what works and what doesn’t. I consulted with a naval architect and got all the answers I was seeking from the trained experts, hence I ended up with exactly what I needed in my boat. Dead rise is just as important as the forefoot of the boat “entry point”. I think way too much emphasis is placed on the dead rise of a hull these days and the forefoot is never even mentioned, yet it’s what pierces the waves and contributes to the overall ride and feel of the boat. By the way, chines do not add to stability when at rest. Beam equals stability how ever chines do add to some of the boats directional stability when underway. Please contact a naval architect flex, you wont regret it.

Stu

[chop duster]

Flex,
First off - what size boat are we looking at here? 6.5m> or <
You say you are looking to venture up past cooktown. Where are you leaving from?
Going North it's more than likely gonna be a following sea. All is good with little deadrise. You spend a couple of days fishing and piss-farting about in partially protected waters. All is good with little deadrise (probably better than a large deadrise).
Then...
Wind starts to blow up. Me starts to think it might be time to go home. Point the bow to a Southern heading (head sea). This is when you are going to wish you bought that boat with that little bit of extra deadrise!
Might not be that much of a help although may get you thinking of your priorities.

[Flex]

Hit the nail on the head there Chop Duster I'd be leaving from cooktown heading north, buggerising around in protected waters,Islands etc and coming home into the famous north QLD trade winds. So doing the trip safely is the biggest concern(I'll be doing it with another boat more often than not)

Plus i'd more often than not be heading offshore from Yeppoon when i cant get up north, whitsundays etc.

[chop duster]

mate if a head sea is going to be part of the norm. I would be looking for some deadrise for sure. 20 and up.
My pick would not be plate ali, but you have prob got your reasons.
best of luck! and may the fish be a bitting

[Wahoo]

HI Flex

talk to your boat builder mate, just tell him what you want/need and they will get it right, its there job, ( boat building) , i know the builders you have posted get feedback on there hulls

best of luck

Daz

[Greg P]

There is a lot more to the hull design than the 23 deadrise on the Fisher. I looked at all those brands and more before I pulled the trigger - in the end it was a no-brainer for what I wanted to do in the boat and where I wanted to do it.