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| 2715 revs, props and stuff in between |
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mark hardy
New member
Username: ebgb
Post Number: 1
Registered: 05-2008
| | Posted on Friday, May 09, 2008 - 02:43 pm: | 
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just bought a new boat, well I say new its a 70 year old scottish fifie, ex herring drifter, she's fitted with a 2715E and a borg warner box, which believe is 1.5:1 reduction.
now, just brought her back down from scotland to the tyne, and think the prop might be totally wrong, or that perhaps there's a governor fitted somewhere to the motor.
max revs about 1650, but that started to sound painful and made little difference to top speed when the revs were at 1500, so thats where we kept her for the run home, 27 hours non-stop, and she never missed a beat, but I would have thought she would rev a bit more, 2250 to 2500 perhaps, which might give her a bit more on the top end. at 1500 revs, with the tide behind us we'd make about 7knots, with the tide against us that would drop to 6 or less. She's 43' LOA, so wonder wether we've got too big a prop holding her back or wether there may be a governor on the engine
she did previously have an old Kelvin K3, which is a very slow revving engine, so maybe the prop from that is still fitted??
any suggestions as to what prop pitch/size should be?? or if there's a governor on the motor, how and where and should I maybe remove it??
mucho thanks, I know, loads of questions for a first post! |
Fred Frog
Member
Username: lilypad
Post Number: 16
Registered: 01-2008
| | Posted on Friday, May 09, 2008 - 03:30 pm: |
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If there is a governor on the engine it will keep you from turning over 1650 when unloaded also. With a warm engine crack the throttle. If it revs over 1650, it should go to 2650, then you know it isn't a governor. (max loaded RPM is 2500 for the 120 Lehman, max unloaded is 2650)
It will not hurt your engine to rev it up to max RPM unloaded for a short period of time.
I think you are overpropped. It may be as you said that it is the old prop, or it may be that someone overpropped it thinking they would get better fuel economy.
K |
mark hardy
New member
Username: ebgb
Post Number: 2
Registered: 05-2008
| | Posted on Friday, May 09, 2008 - 04:37 pm: |
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pretty sure we don't get over 1650 unloaded as well, will give it a go tomorrow to be sure when I'm down there
its possibly both, governor and the prop. Don't think the prop was left for better fuel economy as it went through masses on the trip back, total time at sea was about 40 hours, did about 100 gallons, so 2 and a half gallons an hour at 1500rpm?? |
Fred Frog
Member
Username: lilypad
Post Number: 17
Registered: 01-2008
| | Posted on Friday, May 09, 2008 - 06:01 pm: |
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Not knowing what other conditions exist makes it hard to say if that's a "normal" fuel rate for your boat. (clean fuel, clean filters, back pressure in exhaust, air supply, injector clogged, air in system, etc.)
For comparison, I burn 2.1 GPH in my 120 Lehman at 1750 RPM. My engine will turn up to 2520 RPM while driving the boat. I don't have my notes in front of me but IIRC I can push 7.4 GPH thru the engine at wide open throttle. It moves my semi-displacement 40' trawler hull 2.2 knots faster at full throttle compared to 1750 RPM. In my head math says you were at about 85% of max which would use more fuel.
What we don't know about the economy is what it might be if you weren't pushing the engine. What would it be if you ran at 1400 or 1250? What is hull speed? It might be right about 7 kts. Some boats don't go any faster no matter how much throttle you give it. It's possible that you'd get the same speed at a lower RPM and better GPH. It sounds like a full displacement hull which fits what I'm hearing. |
mark hardy
New member
Username: ebgb
Post Number: 3
Registered: 05-2008
| | Posted on Sunday, May 11, 2008 - 05:51 pm: |
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all filters new and clean, air supply huge - 4" pipe from the manifold straight out of the deck, bled the system, injectors... no idea, exhaust is pretty big as well and again straight out the deck and up behind the wheelhouse
pretty sure there might be a governor on there somewhere, no idea where to start looking though, disconnected the gearshift cables and whacked the throttle right open... 1600ish revs total
hull speed by my reckoning, and knowing a few other boats of this type/shape/size should be around 9knots
I think the prop might be to blame as well, but do think the engine is being held back somewhere |
Fred Frog
Member
Username: lilypad
Post Number: 18
Registered: 01-2008
| | Posted on Sunday, May 11, 2008 - 08:53 pm: |
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Well, we're covering the bases pretty well so far. I suppose the injector timing might be off, or as you say a governor of some type.
Unfortunately that gets out of my skill level. The manual has the instructions on setting the injector pump timing. Find an online manual and give that a try.
You certainly should be able to get more than 1600 RPM with no load.
K |
jefferson wright
Visitor
| | Posted on Friday, May 23, 2008 - 11:01 pm: |
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I have a 2715E 380-ci 1972 ford engine in my boat. The boat is fitted with a raw water pump and heat exchanger with the output from the raw water cooling the wet exhaust. I live in New Hampshire and had my last raw water cooled boat freeze up when I wanted to go fishing. I would like to convert it to dry exhaust. Anybody have any suggestions on what kind of keel cooler or how long/what size of keel pipes to use. also, how is the best way to disable the factory raw water pump on this engine?
Jeff |
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