Wide beam

martinriches

martinriches

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I am thinking of buying a boat that is 32 foot long and 12 foot beam. Will be used for Rivers, estuaries and a bit of coastal. Is such a wide beam more stable at sea? or less so? or perhaps it doesn't make any difference to the sea-keeping. [Displacement hull. GRP. 2'7'' draft]


Martin
 
12ft beam will be fine for all the purposes you have listed.The more beam the better,gives you loads of room at anchor and the ability to move around when underway.
Makes for a very stable boat under all circumstances,the last thing you want is some hull the width of snakes arse which rolls like a pig unless flat out. ;):):)
 
Generally speaking a wide beam is an advantage. Wider beamed boats roll less in a beam sea and they roll less at anchor too. In addition, the wider beam probably means that there is more hull in the water which means it will get blown about less when manouvering. I wouldn't be worried about head sea performance either assuming the boat has at least a moderate V hull. Head sea performance depends as much on overall weight and how well trimmed the boat is on the plane
 
We had a Prestige 32 that was about 33ft and just short of a 12ft beam - planing hull. Absolutely fine at Sea and as stable as other slimmer boats! She was on shafts so did have two enourmous engines nice and central and right down low, which obviously helped, but we never felt unsafe even in a lumpy Sea. What boat is it?
 
Not a boat I know, so will let others give you informed comments on its Sea keeping. It does appear to mainly used for Inland cruising rather than coastal.
 
mjf said:
What has stability to do with beam unless you are discussing deck edge immersion??
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Now we know the exact hull shape ,we do not need to generalise in the answer
It's a wide beam Norfolk / river boat thingy - ( not planning or deep V ) single engine , - no twin shafts to grip" at speed ,it a displacement boat - allready mentioned by the OP
So if a wave approaches at a speed - from any direction greater then the boat speed ( in that direction ) through the water , the greater the beam the bigger surface area to push up - Newtons first law .

Think type 42 frigate- none planning or wind horse for slicing through the water
I suspect there is an optimum length/ beam ratio for displacements vessels re stability ?
I,am standing by my original simple ans in this case
 
"I,am standing by my original simple ans in this case"



You are at anchor and have a beam on sea with wave crests say 3ft apart

A boat with a beam of 12 ft will roll the same amount as a boat with 5ft beam will it ?

Simple example would be to put a 32 ft narrowboat and that broads boat in the same beam on sea conditions and watch what happens
Theory or no theory :)
 
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oldgit said:
"I,am standing by my original simple ans in this case"



You have beam on sea with the waves say 3ft apart

A boat with a beam of 12 ft will roll the same amount as a boat with 5ft beam will it ?

a simple example would be to put a 32 ft narrowboat and that broads boat in the same sea conditions and watch what happens
Theory or no theory :)
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I think we are at crossed purposes here , you I take it are reffering to roll of a static boat ? And that only .
I was thinking more in terms of the boats motion underway in a sea state but at displacement speeds , bobbing up and down too much vertically , than a less beamy boat , as opposed to a more of a "cutting through " the wave hull form .
As I said there will be an optimum L/ B ratio for stability .
Out side this either too beamy or too narrow in the case of a keeless narrow boat in your example will be unsable.
I suspect 32/12 puts it outside.or at the edge ( from a beam perspective ) of this optimum stability " zone" for a seaboat at D speeds in any sort of sea chop. - ,and looking at the pic,s of the hull ,it's designed with Norlfok Broads in mind - emphasis on accommodation over sea keeping .
All boats are essentially compromises , you can,t have it all
So just keep going with the beam - accommodation wise - wider and wider = hello we now got a cat , v wide beam - but perched on on 2x narrow hulls .- reestablishes the golden ratio
 
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Back to the OPs original question. This boat will be fine for river cruising and calm estuary cruising. Excellent for river cruising in fact. But when the going get rough it wont be so good. The boat is likely an ex hire boat with a small engine, perhaps even <50hp.
 
Deleted User said:
Generally speaking a wide beam is an advantage. Wider beamed boats roll less in a beam sea and they roll less at anchor too. In addition, the wider beam probably means that there is more hull in the water which means it will get blown about less when manouvering. I wouldn't be worried about head sea performance either assuming the boat has at least a moderate V hull. Head sea performance depends as much on overall weight and how well trimmed the boat is on the plane
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Displacement hull. GRP. 2'7'' draft
 
I wouldn't be taking that boat coastal. Tidal Thames max. That 35hp BMC will be old and you'll have to thrash it to make headway against a tide and worse with a wind blowing against you. Too much like hard work. Fine for pottering, but that's about it. Made for rivers and IMHO should stay there...
 
"All boats are essentially compromises , you can,t have it all"

Most of the boats around here will mainly be used as day boats for much of the time ,maybe a a hour to get to your favorite muddy creek, a day spent at anchor followed by your hour back home.
Time underway will be small compared to on the move.
The fly in the ointment regards a relaxing day will always be passing craft,especially fast planing craft off somewhere or other,hence perhaps the advantage of a wider boat in the type estuary boating common round these parts.
 
martinriches said:
I am thinking of buying a boat that is 32 foot long and 12 foot beam. Will be used for Rivers, estuaries and a bit of coastal. Is such a wide beam more stable at sea? or less so? or perhaps it doesn't make any difference to the sea-keeping. [Displacement hull. GRP. 2'7'' draft]


Martin
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That is not much over the 3to1 specs for a royal navy design destroyer, I do believe they tend to roll a bit and I know that corvettes do. LOL
 
I am looking for a compromise. I just don't want to get something with two big engines if I am going to spend most of the time in sheltered waters. I am thinking now that this boat is to much of a river boat so I will keeep on looking.


Martin
 
Think that sounds a sensible approach. Perhaps it might be a good idea to ask what peops on here (more experienced than me) might suggest for what you want to do - via a new post. If you describe as you have done and the type of accommodation, area for cruising and budgets etc, you may get some good pointers :)

martinriches said:
I am looking for a compromise. I just don't want to get something with two big engines if I am going to spend most of the time in sheltered waters. I am thinking now that this boat is to much of a river boat so I will keeep on looking.


Martin
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