Davy_S
Well-Known Member
I will still stick with 2.9 knots, half revs remember.
6hp Tohatsu - 3.5 tonne Centaur - speed through flat water
- Thread starter dylanwinter
- Start date
Greenheart
Well-Known Member
Ah. That would probably knock my 5 knot estimate down to 3...
paul-essex
Well-Known Member
3.7 for me 1/2 open 4.6 flat out 
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Rigger Mortice
N/A
I've already bagged that. #7.3.7 for me
Elessar
Well-Known Member
I must have had!
VicS
Well-Known Member
Assuming a 7" pitch high thrust prop and a 2.08:1 reduction ratio in the gearbox at half revs, say 2750 rpm, it should be able to get up to approaching 7.6 knots were it not for the limitation of the lwl
A little less obviously if it has a 6.5" prop
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Lakesailor
Well-Known Member
You are assuming a linear response to prop revs, and that the maximum revs coincide with the perfect balance of prop slip and max hull speed.
My experience of motors in this rev range and boats is that more than half revs (if that) results in lots of noise and vibration, but little increase in speed.
alan_d
Well-Known Member
A spur-of-the-moment decision, perhaps?
VicS
Well-Known Member
Impulse drive is what you will need to power a boat in displacement mode.
To get a Centaur up on the plane you will need warp drive.
MrB
Well-Known Member
Anyone with a guess of 5.2 Knots wins the day. :encouragement:
:encouragement:
JumbleDuck
Well-Known Member
Anyone with a guess of 5.2 Knots wins the day.
5.2kt in one direction, but 4.8kt in the other, so that's an average of (5.2 + (-4.8)) / 2 = 0.2kt. You see? It'll never work.
Fantasie 19
Well-Known Member
+1.. about 3 knots
Blueboatman
Well-Known Member
As 'Tohatsu Urban Leg-End' grows in stature, thrust and bite overnight, I am going to have to go for excellent outside odds:
Gennelmen, the first, the one, the only ( Harbourmasters turn away now please ), the amazing, Harmony goes-like-a-hairy whippet, the forum flier, our very own, intrepid fearless and uniquely British.....The 10 knot Centaur.
Yes!
Yes?
Gennelmen, the first, the one, the only ( Harbourmasters turn away now please ), the amazing, Harmony goes-like-a-hairy whippet, the forum flier, our very own, intrepid fearless and uniquely British.....The 10 knot Centaur.
Yes!
Yes?
Lakesailor
Well-Known Member
So you don't believe Dylan's video?
Fantasie 19
Well-Known Member
So you don't believe Dylan's video?
Damn - didn't know he'd posted it separately... even so.. hats off... clearly that's some engine!
Davy_S
Well-Known Member
That sounded a lot more than half revs!
Blueboatman
Well-Known Member
So what did the video 'say' ?
JumbleDuck
Well-Known Member
A chap I know has done an electric conversion of a Victoria 800, which is not far in size and weight from Dylan's Centaur. It's very fully instrumented, and he tells me that he can do 4kt with 750W electrical power going into the motor, so probably 600W or so at the shaft. It takes surprisingly little power to move a boat at quite a respectable rate; just think of how fast you could walk a Centaur along a long pontoon with the 100W or so available from the average adult. Or, of course, think about the barges which used to ply the canal system with just one horse power (which is about 2/3 of a horsepower) available.
dylanwinter
Well-Known Member
I think that in the pentland we stand a very good chance of clocking up 11 knots over the ground
just imagine what 15 hp in a well could achieve
D
Blueboatman
Well-Known Member
I am sure there's a hearty song in there in the making too
''Oh the night we ran ol' Pentland down.....'' Or better lol