fuel consumption - Page 2

Rickwaines · 31 July 2016, 01:16

The boat moves very well. I love it (aside from docking when it steers like holding a garden hose on full three feet from the end and hoping to direct the water) I haven't had it any weather to speak of yet but it rides very nicely. The leg costs 3 k or so. It might be worth it in the meantime Not sure yet.

idsebby · 01 August 2016, 00:31

How much fuel could you buy with 3 grand. Seems to me unless you are going real long distances stick with what you have?

Or sell the whole engine and buy something that works for exactly what you wanna do.

Depends if it's easier to sell a whole engine or just the jet leg?

Rickwaines · 01 August 2016, 01:49

About 1100 nautical miles worth I think. And therefore, I think the answer is wait till I can buy the right engine. But what is the right engine? 4 stroke or 2? Honda? Merc? Evinrude? I want to have the best fuel economy possible at 20 nauts or so.

beamishken · 01 August 2016, 08:52

Why does the leg cost 3k? Surely a used gearbox could be found for way less than that? If you buy used you could possibly sell your own lower unit for similar money (or maybe even more) I'd imagine the jet lower unit is a rare bird and there may be someone who has to have one who will pay good money for it

idsebby · 01 August 2016, 15:36

Actually yeah not sure what year your engine is but quick eBay search seems you can find them for under a grand.

Rickwaines · 01 August 2016, 16:25

Quote:

Originally Posted by idsebby

Actually yeah not sure what year your engine is but quick eBay search seems you can find them for under a grand.

Somehow I had imagined they would be difficult to find used. Shows my lack of imagination. My engine is a 2005 jet80. What keywords did you use in your search?

Rickwaines · 01 August 2016, 16:53

Amazing. There are so many lower leg units. Hahah of course there are. This is getting good. Noemi just need to determine which one I need and whether there will be enough length in the regular lower unit ornifninwill need to have a spacer ( I have heard that might be necessary) The engine is 2005 2 stroke 115 hp head. Also. If the boat is rated for a max 80 hp motor and my OB (which is currently 80) will be 115 after the conversion, will I have made my rib unsafe?

idsebby · 01 August 2016, 17:34

I say stick with the rating of the boat. I have read that there are insurance issues if you have an over powered boat. A good few threads along those lines.

Sell the jet outboard and buy a new out board suited for your particular boat.

The jet will probably be worth more and you might be able to get a newer outboard or make a few bucks.

But I am still learning so I am sure there are wiser people out there.

Rickwaines · 01 August 2016, 17:46

Right. Insurance. Of course.

Poly · 01 August 2016, 17:53

I'd check with someone that knows their jet outboards, but I'd be surprised if swapping the legs alone gets you 80-115hp. Personally I think your jet o/B is a rare beast that will be wanted by someone with a specialist need, so sell it complete.

Xk59D · 01 August 2016, 18:17

i seem to recall that you lose a lot of HP by going to a jet but would need to google to find that info. however what you are saying rings a bell that 80hp jet is actually like a 120hp normal, need to google as i say.

i would do what the folks above are suggesting, sell that engine and buy another one. you will likely make money if you find the right buyer for that engine.

MickC · 30 March 2017, 23:00

Hi,

I am hoping someone can give me a few pointers regarding the black art of gauging fuel consumption.
I am in a diving club that has an XS700 RIB with twin 100HP Yamaha 4-stroke engines.
We would normally carry 8-10 divers and keep the revs at 4k.
Can anyone give me a rough guestimator at how to gauge fuel consumption.
I will be running a test soon with full tanks and then top up after and do a proper calculation but in the meantime any offers - Just curious!

Rgds.

Mick

Pikey Dave · 30 March 2017, 23:15

Quote:

Originally Posted by MickC

Hi,

I am hoping someone can give me a few pointers regarding the black art of gauging fuel consumption.

I am in a diving club that has an XS700 RIB with twin 100HP Yamaha 4-stroke engines.

We would normally carry 8-10 divers and keep the revs at 4k.

Can anyone give me a rough guestimator at how to gauge fuel consumption.

I will be running a test soon with full tanks and then top up after and do a proper calculation but in the meantime any offers - Just curious!

Rgds.

Mick

Have you got a half decent plotter? If so there will be a trip computer function somewhere that will give you trip distance. Do a brim to brim fuel tank fill & use the trip distance, simples. If no plotter (it's a dive club so I'm assuming you do have one) beg/steal/borrow a Garmin handheld. You can work out the fuel consumption as Nm/l or l/h

MickC · 30 March 2017, 23:21

Tks Dave. I will be doing a proper test once I get the boat in the water - trailer brakes and bearings on the list at the moment. My curiosity was getting the better of me. I saw a rough guestimate on this forim for a single 100HP engine of 1l/KN and was curious or just being plain stupid - Do I just double it??
Mick

Pikey Dave · 30 March 2017, 23:27

Quote:

Originally Posted by MickC

Tks Dave. I will be doing a proper test once I get the boat in the water - trailer brakes and bearings on the list at the moment. My curiosity was getting the better of me. I saw a rough guestimate on this forim for a single 100HP engine of 1l/KN and was curious or just being plain stupid - Do I just double it??
Mick

I had a 6.4 RC with twin 115 Etecs, I used to get 0.7nm/l, it's not as simple as doubling, as each engine wont be working as hard, but you have twice the drag. I'm going to guess at around 0.6nm/l for your boat assuming it's setup & propped correctly.

MickC · 30 March 2017, 23:28

Tks Dave. it could be an expensive season!!

willk · 30 March 2017, 23:29

Quote:

Originally Posted by MickC

I saw a rough guestimate on this forim for a single 100HP engine of 1l/KN and was curious or just being plain stupid - Do I just double it??
Mick

You will be carrying a load of lardy divers and their insanely heavy kit - so I'd say your figures above may well be very close!

I used to run a twin 90hp 6.5m and kept her pretty heavy. She reliably returned 1.44L/Nm at 22-25kts. They were two strokes and you're a bit bigger, so I'd guess that might even out a bit. Allow 2l/Nm and keep a close track of how it goes. Consumption can change easily based on weather/loads/speed/driving style/boat trim/weight distribution, so always use it as a guide and keep a decent reserve. The old cave diving rule applies to fuel too - 1/3 out, 1/3 in, 1/3 reserve.

MickC · 30 March 2017, 23:39

Indeed. Couldn't agree more. Cheers