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Old 22 February 2007, 08:22   #1
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Length and sea keeping question??

We were talking with some friends whether some RIB manufacturers use the same molds to make a hull for a RIB from say 5 to 7 mtrs or from 7 mtrs to 9 mtrs.

We looked at some web sites and we found that one manufacturer does not classify their RIBs as per LOA but as per beam.

We wee wondering whether such construction affects the stability or the sea capability of the boat.

Any one has any ideas??
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Old 22 February 2007, 08:33   #2
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Long and thin is usually what makes a good sea boat - look at things like Revengers - Huntons etc etc.

My boat was made from a mould that made everything from a 6.5m up to a 10m.Looking at the hull shape though the wider parts only really come into play when you turn tightly or are side on in the waves which is what you want anyway.

I take it what you are getting at is should a boat have a custom design for each length you have?
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Old 22 February 2007, 08:41   #3
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Quote:
Originally Posted by codprawn View Post
I take it what you are getting at is should a boat have a custom design for each length you have?
Τhat is the bottom line of my question

My view is that each boat length has certain characteristics for beam, weight and draft also bow and transom angles.

If this is my thoughts are correct for example, a 6 meter boat that comes out from the same mold of say a a 10 mtr boat may not have as good sea keeping capability as a similar boat that came out of a custom made mold.

Am I correct or not? an if not why?
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Old 22 February 2007, 11:36   #4
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Like Codprawn I believe my boat came out of a mould with a moveable Transom section that allows the manufacturer to make several different length RIBs from the same mould.

Its probably why I think my RIB is quite wide for a 6.5M.

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Old 22 February 2007, 12:18   #5
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Quote:
Originally Posted by codprawn View Post
Long and thin is usually what makes a good sea boat - look at things like Revengers - Huntons etc etc.
Long and thin slips right in, but short and thick does the trick .....
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Old 22 February 2007, 12:27   #6
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Hightower you making us assuming things here and you will destroy my thread if we will start speculating
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Old 22 February 2007, 12:33   #7
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Sorry Manos, consider it destroyed
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Old 26 February 2007, 16:13   #8
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something that i have always thought about! Surely with a constant deadrise hull the sea keeping will be similar just hindered by length. However im sure scorpion and scorcerer to mane jus a cople use same moulds for varying lengths! These both both have a warped type hull so does it mean the warp finishes in the same place and a say 8m will only have same varying deadrises as a 6m but with a larger flat area????
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Old 26 February 2007, 16:40   #9
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Convex type hulls (like the Scorpions) allow for such modifications. And although the hulls perform well in rough seaw, the drawback is that they propose a lot in normal sea conditions.

However, other types of hulls IMHO do not allow such modifications and they feel very uncomfortable in most of normal sea conditions.
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Old 26 February 2007, 17:03   #10
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Quote:
Originally Posted by Hightower View Post
Long and thin slips right in, but short and thick does the trick .....
High tower, are you refering to your stature and iQ?????

Should we just call you a "Plug" or perhaps "the wedge"

"It is not the wand, but more so the magician that performs the trick!!!!"
I would add a few happy faces but I dont know how yet....
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Old 27 February 2007, 04:11   #11
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Manos, you started this thread with quite a good couple of posts and then lost it with a quick swipe at Scorpion

Quote:
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Convex type hulls (like the Scorpions) allow for such modifications. And although the hulls perform well in rough seaw, the drawback is that they propose a lot in normal sea conditions.
Really I am assuming you mean "porpoise"

I think congratulations are in order then, because it probably takes quite a bit to make a Scorpion hull handle badly. You would need excessive trim and a badly balanced boat to do it, for example lots of weight in the nose. Since your profile doesn't say Scorpion then it must have been a friends boat, if so were you the excessive weight in the nose? Suggest you advise your friend to do a boat handling course and learn to drive a rib.

Quote:
However, other types of hulls IMHO do not allow such modifications and they feel very uncomfortable in most of normal sea conditions.
Well, you are entitled to your opinion, but I think if you asked a dozen Ribcraft owners they would say there ribs handle sea conditions very well.

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If this is my thoughts are correct for example, a 6 meter boat that comes out from the same mold of say a a 10 mtr boat may not have as good sea keeping capability as a similar boat that came out of a custom made mold.
Possibly, it would be very nice if every manufacturer could design and build different hulls for every size of boat he wanted to sell. Back in the real world costs and time dictate otherwise. If taking a 6.5m rib from a 7m mould produces a hull that handles well in the mind of the manufacturer why not take it to the market place and see if the market agrees with them. A while back you complained about costs of manufacturing in the UK, would you be willing to pay extra for a manufacturer to develop each hull on its own? if so then can I suggest you buy a Scorpion, you never know you might start a new trend and style of driving a rib with porpoising catching on throughout the med

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Old 27 February 2007, 08:13   #12
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Hi Pete,

The Scorpion hull (Bertram design) was an example. There also may be other hulls that have the same/similar aggressive concave (egg shaped) hull design. But that make came first in my head.

Porpoising in calm seas is an effect of this type of hulls what ever you do to them. Everyone knows that. We are making the same discussion again and it may be boring for others

I'm sure that you will agree though that costs in the UK are higher than in Europe in general (not only boat costs) and IMHO it will be reasonable to say that products manufactured in this country are more expensive than products manufactured in Spain, Portugal, Italy, Greece, South Africa, South America, Canada etc. That will apply to boats too I think? I believe is a natural effect and there's nothing wrong with that.

I can't see your point
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Old 27 February 2007, 08:36   #13
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ignoring the left to right hull shapes, how do they allow for the varying deadrise across the entire length of several length of boats out of same mould?
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Old 27 February 2007, 17:48   #14
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Quote:
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The Scorpion hull (Bertram design) was an example.
Do you mean the Scorpion speedboat or the Scorpion RIB?

The Scorpion RIB is a David Marsh design.
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Old 27 February 2007, 18:49   #15
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I think Manos, to address your original question, I'd have to say I've owned 3 boats from the same manufacturer of 3 different lengths. Not all were from the same hull designer, but all were the same width. Unless outright speed is an issue, the characteristics will be largely similar, save for bow angle etc, but for me the difference from a 6.5 to an 8.5 m boat was bigger than any other change I've made. It maybe down to my local coastal prevailing conditions, but I feel I can travel safely so much further in a 8.5m hull than both my previous 5.8 or 6.5 models. Sea keeping made a big advance for me with those extra 2 metres
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Old 28 February 2007, 18:51   #16
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Quote:
Originally Posted by gtflash View Post
ignoring the left to right hull shapes, how do they allow for the varying deadrise across the entire length of several length of boats out of same mould?

no one know?
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Old 01 March 2007, 02:41   #17
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Even on a warped V hull, the varying deadrise is negligible at the rear, and most will be parallel in the last couple of metres so it's irrelevant.
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Old 01 March 2007, 03:16   #18
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So what you say Richard is that what ever the V in the transom is the same mold can be used to build a 6, 7, 8 and 9 mtr even 12 meter boat or whatever length one requires?

But wouldn't be that the length, draft and beam of the boat must be proportionate in order to have good sea keeping characteristics???
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Old 02 March 2007, 19:13   #19
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No Manos, you're stretching the point, as well as the hull! The range 6-12m is clearly not going to produce a great range of hulls from the same mould. And a 6m RIB needs different hull characteristics from a 10m+ RIB, which may need a greater internal beam for the installation of twin inboard engines. However, if you had a mould that you could use for hulls in the 7-9m range, you would probably find that it worked very nicely.
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Old 03 March 2007, 04:28   #20
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Ok ....
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