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semi-displacement hulls


Dearhound

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Just now, Dearhound said:

Hi - a boat with a semi-displacement hull is likely to be more costly to run, fuel-wise yes? Even at slow speeds? Or is it not quite as simple as that? The old Nelsons for example both heavier & with sd hull, would not be very economical I imagine?

More costly to run than what? Full displacement or what? Are you just talking a particular type of vessel here?

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7 minutes ago, Dearhound said:

Hi - a boat with a semi-displacement hull is likely to be more costly to run, fuel-wise yes? Even at slow speeds? Or is it not quite as simple as that? The old Nelsons for example both heavier & with sd hull, would not be very economical I imagine?

No.

 

I had a Fairline with twin Volvo 6-cylinder engines - at fast-cruise (20+ knots) I was getting 1.25 miles to the gallon.

I now have a displacement hull trawler with twin Ford 6-Cylinder engines and at cruise (6mph) I use 10 litres per hour - under 2 litres per mile.

 

It takes a lot of power to push thru water.

 

Its a simple enough formula but basically hull design Vs more Speed = Fuel usage.

 

A semi-displacement hull will get up onto the plane, and once there it will use less fuel. Keep it at displacement speeds (under about 15 mph) and it will use pretty much the same as any other similar sized boat.

Edited by Alan de Enfield
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9 minutes ago, mrsmelly said:

More costly to run than what? Full displacement or what? Are you just talking a particular type of vessel here?

yeah, sorry, more costly than full

7 minutes ago, Alan de Enfield said:

No.

 

I had a Fairline with twin Volvo 6-cylinder engines - at fast-cruise (20+ knots) I was getting 1.25 miles to the gallon.

I now have a displacement hull trawler with twin Ford 6-Cylinder engines and at cruise (6mph) I use 10 litres per hour - under 2 litres per mile.

 

It takes a lot of power to push thru water.

 

Its a simple enough formula but basically hull design Vs more Speed = Fuel usage.

 

A semi-displacement hull will get up onto the plane, and once there it will use less fuel. Keep it at displacement speeds (under about 15 mph) and it will use pretty much the same as any other similar sized boat.

ok, & is there any point in having a semi-d if you are mainly staying inland, that is not heading out to sea to any distance?

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4 minutes ago, Dearhound said:

yeah, sorry, more costly than full

ok, & is there any point in having a semi-d if you are mainly staying inland, that is not heading out to sea to any distance?

As you won't be going above about 6mph on any Inland waterway (canal or River) the boat shape won't make much difference

 

If you are stopping on the canals / rivers then there is not much point having humungous engines guzzling fuel just sat there burbling away.

 

When on the River I generally have to run on one engine to get slow enough - makes steering more interesting.

 

Also - check the draft and air draft of your intended boat.

 

When you have a boat in mind, post it up on here and you'll get some comments.

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11 minutes ago, Alan de Enfield said:

As you won't be going above about 6mph on any Inland waterway (canal or River) the boat shape won't make much difference

 

If you are stopping on the canals / rivers then there is not much point having humungous engines guzzling fuel just sat there burbling away.

 

When on the River I generally have to run on one engine to get slow enough - makes steering more interesting.

 

Also - check the draft and air draft of your intended boat.

 

When you have a boat in mind, post it up on here and you'll get some comments.

Look at this!  Labour of love or what?  Just wondering ....  https://www.boatsandoutboards.co.uk/Offshore-cruisers-for-sale/nelson-34-project-boat-for-refitting-tyler-mouldings-kent-c-/263692?utm_source=newsnow&utm_medium=cpc&utm_campaign=sailboats   LOA 34ft 0in (10.36m)
Beam 9ft 6in (2.90m)
Draught 3ft 3in (1.0m)

 

I think


 

Edited by Dearhound
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1 hour ago, Dearhound said:

I think...…………...

Don't think - it is dangerous (and expensive)

 

Too 'deep' for the canals.

In that condition they should (I'm serious) be paying someone to take it away.

 

This one is "free to anyone who will take it away" and its in far better condition (but shorter)

 

https://www.findafishingboat.com/coronet-24/ad-102630

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25 minutes ago, Alan de Enfield said:

Don't think - it is dangerous (and expensive)

 

Too 'deep' for the canals.

In that condition they should (I'm serious) be paying someone to take it away.

 

This one is "free to anyone who will take it away" and its in far better condition (but shorter)

 

https://www.findafishingboat.com/coronet-24/ad-102630

Yes you're probably right though if the hull were sound enough & if you were prepared to work on it & spend the money, it'd be an interesting boat with loads of history.  

 

I must try to curb my naive enthusiasm & stop looking at projects perhaps.   Looking for a liveaboard so would need to be at least 28ft ish....

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19 minutes ago, Dearhound said:

Looking for a liveaboard so would need to be at least 28ft ish...

I'm very tempted by the 'MOD Motor Launch Liveaboard' (but two boats is enough really)

 

https://www.findafishingboat.com/boat-list/live-aboard-conversion

 

The colours in the bedrooms might need a little 'toning down'.

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Lots of old boats really do not have much future no matter what you do to them. GRP boats are often just mouldings with nothing in them except lots of screw holes from previous lives. The Nelson could just possibly have some sort of future on the French canals but I wouldn't like to be responsible for encouraging anybody to have a go at it.

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10 minutes ago, Alan de Enfield said:

I'm very tempted by the 'MOD Motor Launch Liveaboard' (but two boats is enough really)

 

https://www.findafishingboat.com/boat-list/live-aboard-conversion

 

The colours in the bedrooms might need a little 'toning down'.

You've already got two boats? That's like having two wives. And you are interested in a third?  You need a lie down in a darkened room. (Mind you, if you look at  what you get for your money compared with a narrow boat it is quite interesting)

  • Haha 1
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