Comparisons betwen lumpy water boats and canal boats.

[PaddingtonBear]

As some of you are no doubt aware I have for some time been looking to buy a lumpy water boat, probably a motor sailer or at least a yacht with and good strong engine. One thing that surprises me greatly is the quoted fuel consumption differential between canal and sea boats with similar sized engines - Beta 35, Lister etc even a Bukh 20 or 30. The consumption quoted for sea boats is around 5 times that of inland boats at a similar speed - 3/4kph. Now I know that there are currents and tidal flows but I would have thought that any sea boat is a great deal more efficient than a typical canal floating water tank but from experience these use around 1ltr an hour whereas a 30ish foot Westerley for example with a Perkins 4108 claims (with some pride) to use a gallon per hour. Why? Even Warrior thrashing up the Trent at 10 knots against the tide used only around 1.5 ltrs/hour.

[blackrose]

I always thought it was because sea-going boats had bigger engines, but from what you're saying that's not necessarily the case. I guess they must be getting more power from a similar sized engine if it's using more fuel?

[Timleech]

As some of you are no doubt aware I have for some time been looking to buy a lumpy water boat, probably a motor sailer or at least a yacht with and good strong engine. One thing that surprises me greatly is the quoted fuel consumption differential between canal and sea boats with similar sized engines - Beta 35, Lister etc even a Bukh 20 or 30. The consumption quoted for sea boats is around 5 times that of inland boats at a similar speed - 3/4kph. Now I know that there are currents and tidal flows but I would have thought that any sea boat is a great deal more efficient than a typical canal floating water tank but from experience these use around 1ltr an hour whereas a 30ish foot Westerley for example with a Perkins 4108 claims (with some pride) to use a gallon per hour. Why? Even Warrior thrashing up the Trent at 10 knots against the tide used only around 1.5 ltrs/hour.

 

A few thoughts but nothing to completely explain your query:-

firstly what are your units? kph suggests to me kilometres per hour, but I suspect you really mean knots (which are not 'per hour', a knot is a nautical mile per hour).

Second is that a consumption of that order from a 4.108 would be somewhere near full power, and I can't believe a Westerly would only do 'canal speeds' in open water with a 4.108 going almost full chat.

Thirdly sailing boats often have very small propellers, or 2-blade props or folding props, probably with direct drive, these will necessarily be less efficient than a decent sized 3- or 4- bladed unit, but something described as a 'motor sailer' ought to have something more substantial.

 

Tim

[PaddingtonBear]

Thanks for the reply Tim. I am being vague I know but I have absolutely no recent personal knowledge of lumpy water boats. I obviously mean knots. The disparity seems across the board from 20' weekenders to large Colvic Watsons, none not even the weekenders have an advertised consumption of around I litre/hour, which is what I was getting on the canals in Warrior with a 3 cyl National. I think that perhaps you are somewhere near re. props as most that I have seen are not much better than an egg whisk despite the ability to fit a better engine and large prop. I am going to post this question on PBO forum and will report back.

[ChrisPy]

As far as I recall, the specific fuel consumption of a diesel is of the order of 0.1litres per BHP per hr. The BHP developed is affected to a small degree by the differences in efficiency of the drive system. The only reason the Westerly would have such a high consumption is if it was punching into a head sea in choppy conditions. Otherwise the resistance of the westerly would be no more than a canal boat of similar length and displacement. Of course at higher speeds (say more than about 6 knots) the shorter westerly would be limited by its natural 'hull speed' and the consumption would then rise disproportionately.

[GUMPY]

I have a lumpy water boat that has a beta in it. I usede to have a narrowboat with exactly the same beta in it and guess what. The fuel consumption is the same at the same revs!

 

Caveat

Most narrowboats run at far lower revs than sea boats with the same engine as sea boats have comparatively smaller props I.E. my narrowboat had at 16x12 from memory the yot has a 12x10 so it revs higher but goes faster.

[XAlan W]

I always thought it was because sea-going boats had bigger engines, but from what you're saying that's not necessarily the case. I guess they must be getting more power from a similar sized engine if it's using more fuel?

 

I think you will find that lumpy water boat engines tend to be run at higher revs for much longer periods than canal engines[ie, south coast Portsmouth area to France Cherburg 60ish miles at approx 2750/3000 revs no shutting down for moored boats/locks + engines in narrow boats tend to be in 1400/2000 rev range] + more revs = more fuel consumed

[carlt]

I think you will find that lumpy water boat engines tend to be run at higher revs for much longer periods than canal engines

Exactly.

 

The boatyard owner, where I'm moored, has exactly the same engines in his boat, as me, yet uses twice the fuel.

 

When we went out on his boat together I noted that his engine revs were always around 2500 to 3000, whereas I rarely revved my engines above 1500rpm.

[tosher]

I think you will find that lumpy water boat engines tend to be run at higher revs for much longer periods than canal engines[ie, south coast Portsmouth area to France Cherburg 60ish miles at approx 2750/3000 revs no shutting down for moored boats/locks + engines in narrow boats tend to be in 1400/2000 rev range] + more revs = more fuel consumed

 

I think this is the main reason + smaller props. When we are cruising a section of cut with a lot of locks close together our fuel consumption per hour is considerably less than when we are cruising on a long lock free section.

[larkshall]

Plus of course the prop will not get then same even bite with the roll, pitch and yaw encountered. I often used to run a westerly oceanlord and 75% power for 2 days at a time