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Fuel consumption Merry Fisher 805


Steve S
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I recently bought a Merry Fisher 805 fitted with a Volvo TAMD41A 200hp Diesel.

 

I bought it back round the coast from Cardiff during the trip it used 24 L/Hr overall at an average speed of 12.1 Knots.

 

This was rather more than I was expecting so I was hoping someone knows what I should get out of it and let me know I'll be grateful.

 

Thanks

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We also have an ex Eau salesman in the club "Tom Bettle" he might be able to shed some light on the expected fuel consumption figures.

 

I though would of thought that for a 26' semi displacement boat that 24/25 litres per hour at cruising would be about right

 

Martin

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numbers sound spot on to me.

 

always difficult to be absolutely precise as there will be a number of factors at play with sea state contributing up to 40% variance in some cases

 

Fuel consumption at 8 knots will be vastly better of course - lph and lpm - on a hull/drive train like that.

 

otoh it is a lot of boat for 8m - enjoy it.

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Yep

 

The numbers are spot on.

It won't rise to much more if you pop her up to about 14 to 16 knots, but you'll get that feeling of getting somewhere.

 

It's the hull shape. It's built for very good sea keeping in hard weather rather than it's slender looks!

The rather chubby shape results in a solid boat in the water, but one that pushes a lot of water and hence uses energy (fuel) trying to shove it out of the way.

 

A more planing profile will use less fuel for a higher speed, but this will be at the compromise of the real solid in the water feeling you get from a semi d.

It's all about compromise.

 

I've got the 695 and sure, I'd love another 10 knots on the top speed and 6 or 7 more cruising, but I'd lose all that is superb about the boat.

 

At full displacement speed (6 to 8 knots) your boat will barely sniff the fuel. Anywhere between that and 14 knots the fuel consumption will rise an awful lot as you are pushing a big wall of water. From about 14 knots it will go up, but not the same way it escalated before. Oh, avoid the last 10% of the rev range as it will jump enormously again for only a gain of about 2 knots.

 

Food for thought taught to me by a Weymouth charter skipper.

"A wet boat isn't a bad boat". In fact often it means the opposite. It's right in the water and so it's good and solid. The 805 can be very wet.

 

Expect all semi d's to suffer from weed and slime build up reducing performance during the season.

 

Watch your anodes.

Our South Coast marinas eat them up for breakfast.

 

In my opinion you have bought the best brand of the Pilot House style fisher / cruisers in the sensibly priced bracket.

 

Any questions at all, just ask as I do know them fairly well.

 

Tom

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Thanks for all the info Guys, much appreciated, nice to know it's all working as expected. I'll certainly try running around 16-17knots and see how that goes.

 

One further question, according to Volvo the top power is at 3,900 RPM, in the full speed sea trial the motor was turning over at 4,200 RPM (22.4knots), would that mean a different steeper cut prop could improve performance and reduce fuel?

 

I agree with the comment about her being very seaworthy, we went through some 'interesting' seas around the Eddystone lighthouse and on the approach to Padstow and she handled it all with aplomb. We would have liked a hyperspeed mode for the wipers as it was only after the 3rd stroke we could 'sea' anything.

 

The only thing she doesn't seem to handle too well is a big sea coming from a rear quarter side running about boat speed. She tends to want to turn beam on to the sea then, and did so once, unfortunately we were just off the Skerries at the time so heading straight with the sea was not an option due to the rocks.... Rapid work with the wheel was required. Anyhow it's just a very clear memory now!

 

 

 

 

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Steve

 

They love a following sea if you are brave enough to work the throttle quite hard.

If you have tabs, lift them out of the way in a following sea and try to run faster than the waves.

Power up the face of a wave (you'll sometimes feel like you've almost stopped) at the top ease back on the power so you don't get airbourne and surf down the other side, just faster than the wave.

It's hard to describe, but when you get it right it will just feel right. There will be a sweet spot where she'll feel like she is on a cushion of air.

 

If you are getting 4200rpm she is certainly revving too high.

Check the prop which is fitted as you may need to drop 2" on pitch (certainly 1") although how heavily the boat is loaded will have something to do with this too.

I used to work on about 3850 to 3900 as WOT on the 805 with the Volvo. At that, with a clean bum and sensible load she would be doing +/- 21.5 knots.

 

She'll cruise at up to 18 with the right conditions and load, but do expect fuel consumption to take that next jump up at much over 16 knots.

 

Try it and see and let us know the results. It's been a couple of years since I was on an 805 properly and a couple before that since it was one with a Volvo.

 

Good luck and enjoy and, by the way, welcome to PBSBAC.

 

Tom

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  • 2 weeks later...

Hi Steve,

 

I have been on a work trip abroad and not had much in the way of internet connection so a I am a bit late with a response.

 

If it is of any use to you, my MF805 (fitted with the Nanni engine which is reported to be a bit more frugal than the Volvo option) used to use between 25 to 30 litres/hr at a 17 knot cruise speed. In some reasonably heavy conditions with speed down to 8 knots or so consumption was well below this level (haven't got figures to hand at the moment). The worst figures were on a trip to Cherbourg at the end of last year when consumption rose to about 35 lph due to a "washing machine" sea state and a dirty prop. Makes the 230l tank a bit of a concern - thought I would be needing to refuel at sea at one stage.

 

Well done on bringing the boat around. They are excellent all round boats in my opinion.

 

Alan.

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Steve

..................

If you are getting 4200rpm she is certainly revving too high.

Check the prop which is fitted as you may need to drop 2" on pitch (certainly 1") although how heavily the boat is loaded will have something to do with this too.................Tom

Tom

I think there's a typo, need to increase pitch.

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Steve

..................

If you are getting 4200rpm she is certainly revving too high.

Check the prop which is fitted as you may need to drop 2" on pitch (certainly 1") although how heavily the boat is loaded will have something to do with this too.................Tom

Tom

I think there's a typo, need to increase pitch.

Well spotted Brian.

 

Yes "increase"

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Hi Steve

 

ive got the same boat had from new 4 years now with a TAM 41 VOLVO

like most people on here in the know, all to do with speed and sea conditions

often find when im in a rush back in i can use a lot of fuel so throttle down

mine revs flat out around 3800, i would say 5 gallons an hour would be about right..

enjoy the boat best around for the money. my boats called MIDGE keep an eye out

when your next out and come say hello....

 

cheers kevin

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Thanks for all your input. On this fill up I'm running around the 16-17 knot mark (3,500 Revs) and I'll see what she does.

 

I checked the flat out revs again at it is 4200, so I'll speak to one of these custom prop companies and see what they can come with.

 

I agree think they are a great little boat, I'm really happy with it and so is the wife, unlike the last one. I'm looking forward to getting it out on the rips for the cod and not being worried about the weather to much.

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