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Old 20-04-2011, 01:33   #1
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Cruising at 5-7 Knots in a Power Boat

Can anyone tell me what kind of mileage one could get with a 35-30ft motor cruiser with a single engine in the 250hp range, cruising at 5-7 knots? Mostly flat seas. Any kind of power boat with a decent living space. Like a Cris Craft or something like it. Using it as a displacement.

Anybody ever bough one with a blown motor and put in a small diesel just for cruising?
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Old 20-04-2011, 04:20   #2
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Re: Cruising at 5-7 kots in a Power Boat

I can't help much, but my 10 cents worth 250 hp motor will use around 25 lph 90% power
My 44 foot yacht at 8 kts use about 2 lph
running a diesel motor for long periods of time at low power settings will shorten the life of the motor considerable
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Old 20-04-2011, 04:38   #3
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Re: Cruising at 5-7 kots in a Power Boat

What is the proposed main engine fuel, is petrol or diesel?

Slightly smaller but 25 ft sports cruiser with Volvo 275 hp V8 petrol did 1 litre per mile at about 6.5 knots. It also did 90 LPH flat out but we were travelling very quickly.

Small replacement diesel? our 28 hp in 31 feet does roughly half a litre a mile at 5 knots.

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Old 20-04-2011, 04:44   #4
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Re: Cruising at 5-7 kots in a Power Boat

Depends on the hull design, is it a planing hull type or true displacement? I have had a few 28-32' cruisers that were planing hulls they averaged slightly better at low speeds, roughly 3.5 mpg @ 5-7 , not much worse at lower planing speeds in calm conditions.
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Old 20-04-2011, 06:02   #5
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Re: Cruising at 5-7 kots in a Power Boat

250 HP is a lot for an inboard of that size and to only travel at 5 to 7 knots. Our boat for instance, has a 120 HP and will do 8 to 10 knots but we typically travel at about 7. Our fuel burn is about 2.5 GPH at 7 to 8 knots. It goes up significantly as we increase speed. Our Ford Lehman is quite happy running forever at lower RPMs. Chuck
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Old 20-04-2011, 11:04   #6
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Re: Cruising at 5-7 kots in a Power Boat

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250 HP is a lot for an inboard of that size and to only travel at 5 to 7 knots. Our boat for instance, has a 120 HP and will do 8 to 10 knots but we typically travel at about 7. Our fuel burn is about 2.5 GPH at 7 to 8 knots. It goes up significantly as we increase speed. Our Ford Lehman is quite happy running forever at lower RPMs. Chuck
What kind and size boat do you have. Most 25-30ft I have seen have 2 engines and the singles I could find had 250-350.
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Old 20-04-2011, 11:43   #7
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Re: Cruising at 5-7 kots in a Power Boat

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What kind and size boat do you have. Most 25-30ft I have seen have 2 engines and the singles I could find had 250-350.
Larry, those boats you mention were not designed to go at 5-7 kts. We are talking about trawlers. No one needs 350hp if you plan on going 7 kts with a 35' boat. Try looking at Trawlers, like my 40'er with a 120hp single Lehman. 7kts = 2.3 gal/hr or 3mpg.
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Old 20-04-2011, 11:52   #8
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Re: Cruising at 5-7 kots in a Power Boat

Thats what I have been looking for Trawlers but they are hard to come by in this part of the country most people around here have sail boats. Then I get from some people on some forums that you can cruse the rivers in a sail boat because the draft is too deep. However none of those people actually have cruised the river and they all talk about t he grand loop, even if I never want to do it.

I have read that some people that cruised the river in old Chris crafts with a single engine at 5-7 knots for years. I just wondered if it was possible because they do have the room I am looking for, I have also read about people questioning removing the big engine and installing a small diesel.
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Old 20-04-2011, 11:58   #9
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Re: Cruising at 5-7 kots in a Power Boat

what part of the country are you talking about? What river? Why would trawlers be hard to come by where you are?
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Old 20-04-2011, 12:21   #10
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Re: Cruising at 5-7 kots in a Power Boat

Upper Alabama on the Tennessee river. If I had $100,000 than I could get anything but my budget now is $20k I can do a project boat though.
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Old 20-04-2011, 12:49   #11
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Re: Cruising at 5-7 kots in a Power Boat

here is 4 hits on yachtworld without much trouble. Expand the search territory or price for more

1970 (Power) Trawler Boats For Sale
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Old 20-04-2011, 13:01   #12
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Re: Cruising at 5-7 kots in a Power Boat

25-32ft is what I have been looking for max price $20k so they wouldn't show up on my search which I have done about 20 times. All of those are 34ft and all but 2 over $20k
Although the one thats sale pending looks great. If the sale flops it most likely has big problems. Another problem 120hp I doubt I could get 1/2 gph fuel consumption.
I have also been through 3 other major online broker boat searches and many minor ones.
thank you though.
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Old 20-04-2011, 13:05   #13
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Re: Cruising at 5-7 kots in a Power Boat

good luck in your search.
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Old 20-04-2011, 17:27   #14
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Re: Cruising at 5-7 kots in a Power Boat

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What kind and size boat do you have. Most 25-30ft I have seen have 2 engines and the singles I could find had 250-350.

We have a Marine Trader 34 DC. Click on our Beach House site on my signature line. Chuck
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Old 20-04-2011, 17:57   #15
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Re: Cruising at 5-7 kots in a Power Boat

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We have a Marine Trader 34 DC. Click on our Beach House site on my signature line. Chuck
Yes I could get used to that. No Problem.
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