Bill's boating paradox...
Discussion
Bill said:
pequod said:
Are the kayaks/boards inflatable types??
They are, apart from 1 that I expect we'd do without.FWIW, I use a 12V air pump from Go Outdoors, rather than one of the expensive 'marine' versions available at your favourite chandlery, to inflate my tender. Takes a couple of minutes once the tender is wrestled from the depths of the cockpit locker...
Some rules of thumb for planing boats.
A diesel gives 20hp/hr/gallon
A petrol gives 15hp/hr/gallon
2/3rds speed will burn 1/2 fuel.
So a 30 knot boat with a diesel 200hp engine will burn 10 gallons/hr flat out and at 20 knots 5 gallons/hr.
For a planing boat those are close ish numbers.
Displacement boats use so little fuel its not significant.
Semi-displacement a bit more difficult to generalise.
A diesel gives 20hp/hr/gallon
A petrol gives 15hp/hr/gallon
2/3rds speed will burn 1/2 fuel.
So a 30 knot boat with a diesel 200hp engine will burn 10 gallons/hr flat out and at 20 knots 5 gallons/hr.
For a planing boat those are close ish numbers.
Displacement boats use so little fuel its not significant.
Semi-displacement a bit more difficult to generalise.
Huntsman said:
Some rules of thumb for planing boats.
A diesel gives 20hp/hr/gallon
A petrol gives 15hp/hr/gallon
2/3rds speed will burn 1/2 fuel.
So a 30 knot boat with a diesel 200hp engine will burn 10 gallons/hr flat out and at 20 knots 5 gallons/hr.
For a planing boat those are close ish numbers.
Displacement boats use so little fuel its not significant.
Semi-displacement a bit more difficult to generalise.
Agreed. A Fairline which I was part owner, with twin VP 220's, burnt through 10 gph per engine at 32 knts cruising. I attempted to produce a fuel consumption/revs graph to demonstrate to the others in the syndicate that driving the beast at WOT will require refuelling at sea!A diesel gives 20hp/hr/gallon
A petrol gives 15hp/hr/gallon
2/3rds speed will burn 1/2 fuel.
So a 30 knot boat with a diesel 200hp engine will burn 10 gallons/hr flat out and at 20 knots 5 gallons/hr.
For a planing boat those are close ish numbers.
Displacement boats use so little fuel its not significant.
Semi-displacement a bit more difficult to generalise.
Ref my earlier suggestion to the OP, I just spotted the kind of thing I was wittering about on the 'Bay. 19' with a V6 inboard at 190bhp, a little cuddy to hide or change in, a trailer and pretty tidy. £12k. I know nothing about Maxum although there are plenty pottering around the Solent.
I'm a RIB fan but that's quite a smart thing for the money.
I'm a RIB fan but that's quite a smart thing for the money.
Huntsman said:
For a planing boat those are close ish numbers.
Displacement boats use so little fuel its not significant.
I thought the whole idea of planing was to get the boat out of the water and so reduce resistance.Displacement boats use so little fuel its not significant.
By contrast a displacement hull has to shove tons of water out of the way every second.
So is the reason displacement hulls use less fuel rather because they don't go so fast, rather than they are displacement per se?
Calm down y'all. It was a reference to the 40 knot figure against that fletcher above.
Good luck finding a bayliner with a cuddy in a serviceable condition for 2K - which is where it says the OP's budget might be, above.
Anyway, can see the way this thread is going so I'll leave you guys to it. Good luck with the search.
Good luck finding a bayliner with a cuddy in a serviceable condition for 2K - which is where it says the OP's budget might be, above.
Anyway, can see the way this thread is going so I'll leave you guys to it. Good luck with the search.
Edited by Arnold Cunningham on Monday 9th May 18:37
LFB531 said:
Ref my earlier suggestion to the OP, I just spotted the kind of thing I was wittering about on the 'Bay. 19' with a V6 inboard at 190bhp, a little cuddy to hide or change in, a trailer and pretty tidy. £12k. I know nothing about Maxum although there are plenty pottering around the Solent.
I'm a RIB fan but that's quite a smart thing for the money.
That does look good, although less "practical" looking than I envisaged. I'm quite wary of inboards to, although not for any specific reason. I'm a RIB fan but that's quite a smart thing for the money.
In other news I have a PB2 course booked with eldest son, and SWMBO said "we're just going to have to do it" or words to that effect. Budget discussions are ongoing...
Simpo Two said:
I thought the whole idea of planing was to get the boat out of the water and so reduce resistance.
By contrast a displacement hull has to shove tons of water out of the way every second.
So is the reason displacement hulls use less fuel rather because they don't go so fast, rather than they are displacement per se?
Simply, the power goes into making waves.By contrast a displacement hull has to shove tons of water out of the way every second.
So is the reason displacement hulls use less fuel rather because they don't go so fast, rather than they are displacement per se?
Pure displacement is slow. 'Hull speed' in knots is about 1.4x the waterline length in feet, trying to go faster than that without planing uses lots of power.
Our club RIB, when well loaded you can feed in a lot of power, it will struggle to get on the plane, but once it's planing, you can back the throttle right off.
It gets complex because propellors are complicated things, if the prop is poorly matched it can be very inefficient.
Hulls designed to plane can be rubbish at low speeds, dragging a submerged flat transom
Big complicated subject, one thing to take away is that a boat engine runs at a high% of nominal power for hours on end, compared to a car.
My car cruises at 60mpg doing 60mph. 1 gallon an hour that's about 20HP from a 160HP engine. My little boat cruises at between .8 and 1.2 litre an hour, maybe more in rough weather, from a 14HP diesel, and it's expected to do that all day or night continuously. A 40HP outboard is likely about 800cc, not much like a bike engine!
OutInTheShed said:
Bill said:
To save distracting the shoestring sailor thread...
We're near Swanage and figure it's mad living here and not having a boat.
We're after something to take kids & kayaks/paddle boards further afield to access more interesting areas. For example, we can get to Old Harry's rocks from Swanage or Studland but it's a slog with a pair of double kayaks and towing one more. Kimmeridge is fine, if a bit limited but Lulworth is a slog getting everything to the water, Worbarrow is a mission and a half!
And we'd like to tow a ringo, and even a skier... Want a cabin (cos girls...) And he icing on the cake is that SWMBO doesn't want noisy!
Plus we're both tight and I'm wary of ending up with a money pit.
Experience wise we do a fair bit of sea kayaking, I have done a sailing day skipper ticket but not used it and holidays as a kid involved clueless use of small boats in Cornwall a fair bit. I plan to do PB2 and my VHF ticket this year.
1) all boats are money pits.We're near Swanage and figure it's mad living here and not having a boat.
We're after something to take kids & kayaks/paddle boards further afield to access more interesting areas. For example, we can get to Old Harry's rocks from Swanage or Studland but it's a slog with a pair of double kayaks and towing one more. Kimmeridge is fine, if a bit limited but Lulworth is a slog getting everything to the water, Worbarrow is a mission and a half!
And we'd like to tow a ringo, and even a skier... Want a cabin (cos girls...) And he icing on the cake is that SWMBO doesn't want noisy!
Plus we're both tight and I'm wary of ending up with a money pit.
Experience wise we do a fair bit of sea kayaking, I have done a sailing day skipper ticket but not used it and holidays as a kid involved clueless use of small boats in Cornwall a fair bit. I plan to do PB2 and my VHF ticket this year.
Forget the alleged lack of depreciation, cost of ownership tends to be high.
Storage, trailer parking, insurance, hardware, repairs, all have 'marine tax' in the price.
2) To get value, you have to use it. A lot.
3) The money that gets eaten by boats is dwarfed by the time they take up. Launching a boat takes time, recovering and putting it away takes time. There are always things to do which take time. Getting anywhere by boat takes time.
4) Fuel economy is measured in gallons per hour and that can make you resent the hours. You have to have the right mindset to enjoy burning £50 of fuel going around in circles for a few hours, let alone £250. But most people end up looking back at the last year thinking fuel wasn't the half of it, we didn't use it much and the fuel was dwarfed by fixed costs.
OutInTheShed said:
Simpo Two said:
I thought the whole idea of planing was to get the boat out of the water and so reduce resistance.
By contrast a displacement hull has to shove tons of water out of the way every second.
So is the reason displacement hulls use less fuel rather because they don't go so fast, rather than they are displacement per se?
Simply, the power goes into making waves.By contrast a displacement hull has to shove tons of water out of the way every second.
So is the reason displacement hulls use less fuel rather because they don't go so fast, rather than they are displacement per se?
Pure displacement is slow. 'Hull speed' in knots is about 1.4x the waterline length in feet, trying to go faster than that without planing uses lots of power.
OutInTheShed said:
Big complicated subject, one thing to take away is that a boat engine runs at a high% of nominal power for hours on end, compared to a car.
My car cruises at 60mpg doing 60mph. 1 gallon an hour that's about 20HP from a 160HP engine. My little boat cruises at between .8 and 1.2 litre an hour, maybe more in rough weather, from a 14HP diesel, and it's expected to do that all day or night continuously. A 40HP outboard is likely about 800cc, not much like a bike engine!
I seem to be the other way round. My boat has a 3-cylinder 40hp inboard diesel which spends most of its time at 1600-2200rpm, using very little fuel. However my 12-cylinder 450bhp car only manages 18mpg!My car cruises at 60mpg doing 60mph. 1 gallon an hour that's about 20HP from a 160HP engine. My little boat cruises at between .8 and 1.2 litre an hour, maybe more in rough weather, from a 14HP diesel, and it's expected to do that all day or night continuously. A 40HP outboard is likely about 800cc, not much like a bike engine!
So you see the boat offsets the car's emissions
Huntsman said:
Power = the rate of doing work.
In this instance work = moving the boat.
Faster you go the more fuel burn.
Regardless of hull type, more speed = more fuel, there are no free knots to be had regardless of hull type.
If it was as simple as that, the 'work' in going from A to B would be the same whatever speed you went, so you'd use the same fuel going the same distance, just in different times.In this instance work = moving the boat.
Faster you go the more fuel burn.
Regardless of hull type, more speed = more fuel, there are no free knots to be had regardless of hull type.
Work = Force x Distance
What you need is a graph of force, i.e. hull drag, against speed.
Classically, drag is low at low speeds, rises quickly as you get near hull speed, then reduces as you 'get over the planing hump', then steadily rises.
In real life, bashing into waves adds lots to the power needed.
And props have interesting efficiency curves as a function of speed and thrust/drag.
In my world, you can sometimes save a lot of fuel by opening the throttle and getting around the corner before the tide turns.....
Or you can use a fair bit of power going nowhere against the tide....
pequod said:
I realise it's well above your initial budget (we are well known on here for helping you with the man-maths!) but a Merry Fisher such as this one would be a better bet and they have a good reputation for a reason...
https://www.boatsandoutboards.co.uk/boat/2010-jean...
I know it's an ex fishing boat (most will be at this price point) but it does everything you want and has that all important cabin and a decent E-tec outboard by the look of it! I would rather have a boat that has been regularly used and maintained instead of something which might require a bit of money spent on servicing/refit having sat around unused and unloved for a few years.
P
Sorry to hijack the thread but something like that boat is very much what I am considering buying (size/budget/type), but I keep coming back to how/where to store the thing (I live on the Somerset/Devon border). Am I right in thinking that my options are:https://www.boatsandoutboards.co.uk/boat/2010-jean...
I know it's an ex fishing boat (most will be at this price point) but it does everything you want and has that all important cabin and a decent E-tec outboard by the look of it! I would rather have a boat that has been regularly used and maintained instead of something which might require a bit of money spent on servicing/refit having sat around unused and unloved for a few years.
P
Edited by pequod on Thursday 5th May 14:29
1 - Expensive marina if I can find one (£4k/year)
2 - Somewhere up a river but still in the water (maybe £2,000/year?)
3 - In a boat yard near a river on a trailer and launch it as and when (maybe £1,500/year)
4 - In a boat yard not at a river (£1,000 year perhaps)
I accept that towing/launching is a pain, but going down that route does mean being able to take the boat to plenty of places and I assume anti-fouling isn't required. I have a RAV4 diesel which I assume would tow it without too much trouble.
Cheers :-)
Might be a bit far for you though : https://www.lrpbc.co.uk/
Generally, you want to make it as easy as possible to use - but that can mean different things.
For me that means keeping it at home so I can tinker & maintain it ready for use when I want to.
But for many people that'd mean keeping it afloat in a marina and turning the key and going each weekend.
Worst thing would be to leave it in the water at a marina and not use it.
With a little practice, it's easy to trailer launch quickly and easily. I used to keep one of my old boats on the shore at a marina for the summer and that worked well - and I'd self launch to save money too. That seemed like a good balance of price vs flexibility at the time. Although the following season I kept it at home and trailered it down. Consequently I used it less, too.
Generally, you want to make it as easy as possible to use - but that can mean different things.
For me that means keeping it at home so I can tinker & maintain it ready for use when I want to.
But for many people that'd mean keeping it afloat in a marina and turning the key and going each weekend.
Worst thing would be to leave it in the water at a marina and not use it.
With a little practice, it's easy to trailer launch quickly and easily. I used to keep one of my old boats on the shore at a marina for the summer and that worked well - and I'd self launch to save money too. That seemed like a good balance of price vs flexibility at the time. Although the following season I kept it at home and trailered it down. Consequently I used it less, too.
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