Best type of hull shape

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steve the farmer

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Again please excuse my ignorance about asking these questions, but if you looked at my other couple of threads you will know I am looking to buy my first boat, but know not much about them yet, other than using/riding on ribs. So before I buy I am on this steep learning curve, doing plenty of research and asking questions, some of which may appear to those in the know, stupid questions, like this maybe.

I have basically decided its going to be a trailer-able craft so about 25' GRP and no more than 2500kg, so I keep to my 3500kg limit with trailer and fuel. Mostly used for family days out, some fishing, possibly some scuba with my buddies, so Ideally a sport cruiser, but there is a BUT!

I note that most planing hulls use a 5L or 5.7 V8 Mercruiser or Volvo petrol engine and Diesel engine versions of this type family weekend cruiser are like rocking horse S--T. Presumably the diesels just do not have the performance of the petrol engines for planing?
I would prefer diesel, I just know diesel engines better than petrol, I have tractors and other diesel powered plant, and would just feel more comfortable with a less volatile fuel on the water. Plus, to me diesel fuel is 1/3rd the cost of petrol at the pump. Although I am aware we have a Customs and Excise requirement to declare reduced tax rate fuel used for pleasure craft here in the UK.

But my real question is, whatever fuel the boat uses, what do these 21-27' planing hulls travel like at low speeds, say about 8 - 15 knots, and is there a big reduction in fuel used at low speed or is travelling at low speed with a planing hull in coastal water uncomfortable?

I am just thinking that a) my wife will not want to be powering along at 25-40 MPH all the time, and b) that will only give us limited time on the water before we are out of fuel. And she would rather chug along at 15 knots all day anyway, and I would also rather be out all day cruising the coast rather than a whiz around the bay if you know what I mean?

So if I cant find a quickish diesel cruiser and we went with a petrol 5l V8 and a planing hull, giving about 25 knot cruising 35 -40 top speed, is it a realistic expectation that we could go all day at say 10-15 knots, make a huge saving on fuel without feeling like I have been tossed side to side in a tumble drier because we have not been planing?
Or should I be looking for a deep V hull and a plodding diesel engine. However, I am certainly not wanting to buy a 6-8 knot fishing boat though, I do really want a weekend family type cruiser but will accept a top speed of 20-25knots.

It will probably be a a boat built in the 1990's or early 2000's as my budget is under £30.000. Ideally around the £20k mark.

Thank you
Steve.
 
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Generally small planing cruisers cannot travel between 8 and 15knts at all, if they do the bow is pointing at the sky as its trying to climb over the hump to start planing and using loads of fuel. So in reality you can do up to 7-8knts or more than 15knts but nothing in between, if you want to travel at those speeds you need a semi displacement type hull.
 
Our 25ft boat is diesel and weighs in at 2400kg dry weight.

As others have said in a planing boat anything above 6 knots is a waste of fuel. You are either on the plane or plodding along at displacement speeds.

The lowest speed ours is happy planing at is about 20 knots. It tops out at 30 knots.

We use our boat on a mix of canals, rivers, estuaries and the coast so it has a good old mix of slow speed cruising as well as higher speed cruising.

Our fuel economy averaged out over last year was 5.4mpg which accounts for a mixture of river and coastal cruising. We have a single Volvo Penta KAD32 which has been very reliable over the last 9 years that we have had the boat. Can't fault it really.

You should get a decent diesel S23 for under £30k. There are a selection in the link below:

http://www.newsnow.co.uk/classifieds/boats-for-sale/sealine-s23-for-sale-uk.html

Don't be afraid to haggle on the asking prices.
 
"So in reality you can do up to 7-8knts or more than 15knts but nothing in between"

Id disagree massively with this, i currently have a 25 foot planing boat (with diesel engine) and it will do any speed you want. Every other boat i have owned or driven has also been happy enough at any speed, not as happy as a semi displacement boat,but happy enough to be usable. And obviously they have sweet spots ,usually around 5-10knots and 20-30 knots,but to say you cant do any other speed ia misleading

You can certainly go all day at low speeds if you want,but if that is your primary use case you would be better off with a semi displacement boat.
 
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Can't improve on #4 note. I would say that this will be a big rig to tow regularly. I towed a 25ft sports cruiser once, and was not at all comfortable doing it.
 
julians said:
"So in reality you can do up to 7-8knts or more than 15knts but nothing in between"

Id disagree massively with this, i currently have a 25 foot planing boat (with diesel engine) and it will do any speed you want. Every other boat i have owned or driven has also been happy enough at any speed, not as happy as a semi displacement boat,but happy enough to be usable. And obviously they have sweet spots ,usually around 5-10knots and 20-30 knots,but to say you cant do any other speed ia misleading

You can certainly go all day at low speeds if you want,but if that is your primary use case you would be better off with a semi displacement boat.
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Can I ask what boat you have?
 
rafiki_ said:
Can't improve on #4 note. I would say that this will be a big rig to tow regularly. I towed a 25ft sports cruiser once, and was not at all comfortable doing it.
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I am not fussed about the towing, as long as it is legal. I have a farm and have towed some really big stuff. And where I am in the middle of Kent, I only need to travel 1hr in any direction to reach either North Kent coast, South Kent coast, the Thames estuary or the River Medway. Any long distance may be once twice a year.
Thanks.
 
julians said:
Its a windy 25 mirage.
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With what engine?

Guessing it is nothing supercharger.

Get above 1500rpm with our KAD (which is about 6 knots) and the supercharger kicks in. This kicks the bow in the air, creates a massive wash, uses a frightened amount of fuel for not a lot more progress and is a sure fire way to deafen your self!

Yes you can sit at 10 knots if you have to. But you wouldn't want to make a habit of it.
 
With a volvo penta d4,so it has a super charger and turbo. No issues with putting bow in the air,just use trim tabs to keep the front down
 
Have you looked at second hand Arvors? These are diesel powered fishing boats, not a great deal of luxury for the family, just make sure the VW turbo has been fixed
 
Just about to say that.... arvor / quicksilver are in that range. I have a 7m 150hp vw quicksilver semi displacement hull. I haven't owned it long enough to comment on fuel etc.
 
In your situation with just about ever bit of plant surrounding you being topped by very probably your own fuel supply,the word petrol should not even be entering the conversation.
With supermarket petrol at over £5.00 per gallon and Marina stuff at £7.00 suspect your price per litre for diesel will make some of us weep.
Our club diesel is around £3.50 a gallon at the moment..
...and if you need a boat club to join that actually goes places we have several peche promenades of all flavours on the fleet....:)
 
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