speed with diesel?

joakimhansson · 16 September 2005, 20:25

How fast is a diesel compare to a outboard? If you take mercrusier 1,7 and a outboard with around 115-125 hp.

And the bigger yanmar/volvo...

Can you get close to 50 knop with a 315 yanmar, on a revenger 27-29 (or simular boat).

For me diesel is slow....but you can change me...??? or..

And offcause fuelconsumtion?

Mollers · 16 September 2005, 23:11

Speed with diesel?! Not tried it, sounds far out man! Tried Coke and Asprin once, that was crap.

Got rid of my head-ache though

codprawn · 17 September 2005, 03:10

Have a look at the EPS Tigershark - a Mark Pascoe design -

http://www.epsmarine.com/html/frames/fr_1.html

Don't know top speed but would guess maybe 65mph??? It has a surface drive!!!

Mike C · 17 September 2005, 10:14

Quote:

Originally Posted by joakimhansson

How fast is a diesel compare to a outboard? If you take mercrusier 1,7 and a outboard with around 115-125 hp.

For me diesel is slow....but you can change me...??? or..

And offcause fuelconsumtion?

You will probably go faster with the 115 o/b in this comparison. I think I am right in saying though that the Merc 1.7 is 120hp 'at the engine'.... so by the time you reach the prop it is probably nearer to 100hp. The outboards will be rated 'at the prop'. My Humber Ocean Pro with the Merc 1.7 has a top speed of around 30 knots and cruses nicely at about 23 knots. (GPS readings) Not a race winner but a good cruiser.

Outboards are lighter than diesels so they will always have more 'go' than a similar powered diesel but that doesn't mean you can't get a fast diesel set-up. You'll just need a bit more horsepower I presume! (No doubt some engine expert can give us some comparison figures on that)

However, don't cast aside the thought of diesel. There are 3 very good reasons for considering it. (Even without the current price difference in the UK)

1) Fuel economy. I recently did 2 days cruising around the Scottish Islands, logging up 130 miles on the GPS. I refuelled to a full tank with 95 litres of diesel. That’s 0.73 of a litre per mile!

2) Fuel Availability. Diesel is far more easily available at the dock than petrol, (in the UK anyway).

3) You are not sitting on a bomb! If your boat catches fire, at least you have a chance of putting it out with diesel!

Always diesel for me from now on! The Merc 1.7 is a nice little engine but there are now similar sized, more powerful engines available.

Mike C

DGR · 17 September 2005, 10:57

My Ribcraft 7.8 has got the 315HP Yanmar engine with a Bravo 2 leg, and can just about get to 40 kts (GPS) on a flat day. It is a heavy boat though, so something lighter might go a bit quicker.

Over the summer (250 hours) I've got through between 10 and 20 litres of diesel per hour - depending on what we are doing. The 20 litre days are the ones where I spend most of my time at max continuous revs (3600 rpm)

.

Hope this helps!!

D...

simmons0 · 17 September 2005, 11:51

With our Merc 1.7 we get 40 knots flat out and cruise it around 28knots, Mike, its 116hp at the prop and a bit over 120 at the crank.

Alan Priddy · 17 September 2005, 12:58

You should have a look at the new Yamaha 315 plus Twin Rotating Prop system. Engineering excellence. All new and will proberbly be the world leader within two years. But then what do I know? Alan P

codprawn · 17 September 2005, 14:43

Of course you are not biased

Taken from the Yamaha website

"The 2005 Southampton International Boat Show has been chosen to host the world launch of the new Stern Drives range, which just goes to show how important the UK market is for this type of engine...
Or perhaps its because we Brits know a thing or two about good engineering, just ask Alan Priddy, he successfully took his single engined Yamaha ME420 powered Spirit of Cardiff rib for a record breaking circumnavigation of the globe..."

It does look like a a very interesting package though - wonder what the weight will be like???

Jonny Fuller · 17 September 2005, 15:36

Quote:

Originally Posted by Alan Priddy

But then what do I know? Alan P

How to blow your own trumpet?

The Garfish · 17 September 2005, 16:40

Quote:

Originally Posted by simmons0

With our Merc 1.7 we get 40 knots flat out

Quote:

Originally Posted by simmons0

we hit 43knots

Quote:

Originally Posted by simmons0

I get 45knots

Quote:

Originally Posted by simmons0

we hit 47.7knots

fuk mee simmuns1 i fink yew mus av a derty bottum de waiy yorr bote iz lewzin spead

gArf

Mike C · 17 September 2005, 18:59

Quote:

Originally Posted by simmons0

With our Merc 1.7 we get 40 knots flat out and cruise it around 28knots, Mike, its 116hp at the prop and a bit over 120 at the crank.

Seriously, is that from the GPS or a paddle wheel 'speedo'? I can get nearly that on the paddle wheel... with the boat on the plane and the paddle wheel spinning half out of the water.

My Humber is a fairly heavy boat so I'm sure a faster design would get a few more knots.... flatter hull, higher plane position etc but an extra 10? I keep hearing these great figures for the Merc 1.7 but I've never seen it. The speed I quoted is the average reading I get, depending on current and tide obviously.

So how did you measure it?

Mike C

IanE · 17 September 2005, 19:50

6.3m with the mercruiser 1.7

Since I fitted trim tabs (and cleaned the tubes) about 34-35kts top and cruise at about 28kts I think Andre got about the same

Ian

Andre · 17 September 2005, 20:52

Simmoms0 has a Solent 6 mtr much lighter then Mike's Humber 630 and Ian's Parker 630 hence I guess better top speed.

I recently tested the Parker 750RS fitted with the Cummins Mercruiser 4.2 (320HP) linked to the B3 drive. Top speed on a lake 46 knots. With diesel you can enjoy speed. This is my rib for 2006

simmons0 · 18 September 2005, 00:46

Quote:

Originally Posted by The Garfish

fuk mee simmuns1 i fink yew mus av a derty bottum de waiy yorr bote iz lewzin spead

gArf

Yeah thats how it went GaRf, the day we got it the max speed on kevin's hh gps (with him driving) said 47.7 knots, havent seen that since, but it will do 40knots gps speed.

Mike, 40 knots is an average top speed, it's done 43knots with 1 person and maybe some tide but if i took you out for a spin i could guarantee you'd see 39knots and it should touch 40.

bogib · 18 September 2005, 00:54

Quote:

Originally Posted by simmons0

Yeah thats how it went GaRf, the day we got it the max speed on kevin's hh gps (with him driving) said 47.7 knots, havent seen that since, but it will do 40knots gps speed.

Mike, 40 knots is an average top speed, it's done 43knots with 1 person and maybe some tide but if i took you out for a spin i could guarantee you'd see 39knots and it should touch 40.

Or he will read 49,9 knoths to beat all others......

Bogi

bogib · 18 September 2005, 00:57

I may be able to add something to this as finally the Blue Arctic RIB are finally due to be out of customs bond on Monday and that one is powered by 320 hp Cummins/Mercruiser diesel and I and my colleage will have a ride on Monday or Tuesday pending on when put on water ... somebody have to do the warranty work

Bogi (warranty inspector

)

Mike C · 18 September 2005, 10:26

Quote:

Originally Posted by simmons0

Mike, 40 knots is an average top speed, it's done 43knots with 1 person and maybe some tide but if i took you out for a spin i could guarantee you'd see 39knots and it should touch 40.

OK, may take you up on that one day! Is your's the 6.0 or the 6.5? I've just had a look at the 6.0 and with the extra tube length, (Humber's tube extension at the stern is very short - so more hull for given LOA), I would guess I had getting on for half a metre more hull than that one. That may be the extra weight... or maybe mine is just a heavier lay-up? I know my boat and Andre's original Seahawk did about the same top speed. Well, he just pulled away from me but he again had slightly less hull and a S/S prop.

What prop are you running, (and pitch). I'd be interested to know. (Aren't Solent Ribs, Lee Fairweather's baby? I know he did a lot of speed work on the Merc 1.7 when it came out.... and he won't use S/S on the Alpha One leg. Maybe he has the secret... Eh Lee?)

Mike C

brucehawsker · 18 September 2005, 11:08

Funny. The fastest I ever got Farfetched, well actually second fastest but that second one was with a real tidal run, was with Kev from Solent on her maiden test run. We were parallel to the shore on the Western approach to Portsmouth going NE. Is there a strong helpful run there? Is that Kev' s little secret???

I get 42 with full fuel 4 passengers, no probs. Have seen 46.7 with two up and half tank. These on GPS averaging two runs in both directions (48.7 one way and 44.7 other).

Incidentally, fuel has settled down to 1.1/1.2 l / Nm, about 15 litres an hour, 2 stroke oil consumption very modest. Range (safe) is about 100Nm on the 160l tank - usable about 135 I reckon.

simmons0 · 18 September 2005, 14:06

Ours is a 6m, and yer, Lee has always told us not to bother with a stainless prop, because we were keen to try one.
At the moment its a 23p Ali prop, but its slightly worse for wear hence the drop in speed from just over 40knots to just under.

We fitted some doelfins a few weeks ago too, worked wonders. Flies more level now, quicker onto the plane, more responsive to the trim, cavitates less, no drop in speed at all.

bogib · 18 September 2005, 14:14

Quote:

Originally Posted by simmons0

We fitted some doelfins a few weeks ago too, worked wonders. Flies more level now, quicker onto the plane, more responsive to the trim, cavitates less, no drop in speed at all.

I have never seen Mercruiser with doelfins do you have pictures ?, I can lent you a SS prop to try out if you want, can bring it over soon as I need to have a look at my new boat shortly not that far from Kenilworth.

Bogi