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Thread: marine diesel vs gas for jet boat

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    Default marine diesel vs gas for jet boat

    I am going to repower my jet boat for next year. I have a 20ft Wooldridge extra plus with a 351 and a Hamilton 773 right now. I am familiar with the 350 and can easily swap motors and upgrade to fuel injection. I am over the Ford marine motors, parts are getting hard to find. We were talking on our long boat ride on the yukon and talking about diesel motors. They are built for long running with lots of torque to haul heavy loads. Just the ticket for the Yukon. We thought the draw back would be the hole shot and top end speed maybe. The other draw back may be field maintenance, but we were not sure if it would be better or worse than the 350. Oh yea, and the price. Does anybody have an opinion on diesel vs gas that could give some insights on performance, maintenance and cost effectiveness? I emailed FNM Alaska and they said that their 250 HP model will give similar performance to the MPI 350 with 3 gal per hour fuel savings.

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    Member broncoformudv's Avatar
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    You will also need to step up to a bigger jet unit. Either a Hamilton 212 or 241 depending on the diesel or repower you go with. There is a guy on the Yukon that frequents this forum that repowered his Wooly with a diesel but I can't think of his name right now. If you do a search it should pop up with something about it.

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    Default marine diesel vs gas for jet boat

    Saved I ran 250 FNM Diesel this spring. Pretty dam impressive. I say go with the diesel.
    Do I give my friends advice? Jesus, no. They wouldn't take advice from me. Nobody should take advice from me. I haven't got a clue about anything..

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    Something else to think about specific to the Yukon, is access to diesel. On my trip last year to the Koyukuk, I didn't recall seeing diesel besides in Ruby and Galena. So you'll need to maybe carry more on board. Besides that I've heard good things about the FNM's. + 1 for upgrading your pump to a 212 also, so add another 9-12k for that. Good luck on your choice.
    Tony

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    Quote Originally Posted by tzieli22 View Post
    Something else to think about specific to the Yukon, is access to diesel. On my trip last year to the Koyukuk, I didn't recall seeing diesel besides in Ruby and Galena. So you'll need to maybe carry more on board. Besides that I've heard good things about the FNM's. + 1 for upgrading your pump to a 212 also, so add another 9-12k for that. Good luck on your choice.
    I asked FNM if you could use alternative fuels such as heating oil or Jet a. No response yet but that is definitely a consideration

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    Member alaskabliss's Avatar
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    With the cost of a complete diesel and jet swap you might be better off getting a new boat with all the fixens. I would think that the diesel would be better in a 22'+ length boat.
    Figure in the cost to repower and re-jet at $25-30k compared to just a new MPI 350 for $8K. How much fuel savings would it take to make up that difference?

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    In my opinion none of those small lightweight, high rpm diesels will push heavy loads for any amount of time. I saw how quick the volvo diesels wore out, broke down & blew up in the bowpickers pushing ice and fish around, hell they wore out quickly just running light boats !!! I'd stick with the gasser maybe just go with more horsepower and don't run it as hard.

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    Quote Originally Posted by tzieli22 View Post
    Something else to think about specific to the Yukon, is access to diesel. On my trip last year to the Koyukuk, I didn't recall seeing diesel besides in Ruby and Galena. So you'll need to maybe carry more on board. Besides that I've heard good things about the FNM's. + 1 for upgrading your pump to a 212 also, so add another 9-12k for that. Good luck on your choice.
    Diesel is available just not directly via a hose at the river. I purchased heating fuel in Tananna last year at the General Store for $1 less then the gas at the river pump. We just had to take our drums up to fill them from the tank. They let us use their truck to haul the cans down to the boat. Although the 212 is definitely a better work horse the 773 should do well with the correct impeller setup.

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    when comparing performance, wouldn't the diesel and gasser be equal if they both spun the same impeller at like rpm's?....so to increase performance wouldn't you need to spin a higher pitched impeller regardless of power plant?

    when comparing longevity/economy, wouldn't the diesel have an upper hand?

    when comparing cost/simplicity, wouldn't the gasser have a tremendous advantage?
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    Quote Originally Posted by Halibutgrove View Post
    Diesel is available just not directly via a hose at the river. I purchased heating fuel in Tananna last year at the General Store for $1 less then the gas at the river pump. We just had to take our drums up to fill them from the tank. They let us use their truck to haul the cans down to the boat. Although the 212 is definitely a better work horse the 773 should do well with the correct impeller setup.
    Mel,
    Will those diesels run ok on heating oil?? or do they run better/live longer on the new low sulfur fuel ?? just askin'

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    I think the cost is the biggest issue myself. Heating oil, road diesel and the like should burn fine and are readily available. Diesel motors are supposed to last much longer and that is good when you are taking it down the Yukon every year. I want to overload my boat, so I want as much push as I can reasonably get, speed is not as important to me as keeping a good load on step. My other alternative is to buy a new to me wider boat and then start over. I will be running into the same problems as I am on all my other boats, used gear that is being pushed to it's maximum. I really can't afford a new boat. My ideal would be a 70+" extra plus, 20 ft long with this diesel in it. Suspension seats and 6 foot top. Hey Glen, do you make such a beast?

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    Quote Originally Posted by tjm View Post
    when comparing performance, wouldn't the diesel and gasser be equal if they both spun the same impeller at like rpm's?....so to increase performance wouldn't you need to spin a higher pitched impeller regardless of power plant?

    when comparing longevity/economy, wouldn't the diesel have an upper hand?

    when comparing cost/simplicity, wouldn't the gasser have a tremendous advantage?
    I still don't get the impeller pitch, Nozzle size, Kilowat, torque curve, RPM, turbo impeller multi or single stage debate. Every time I think I do, it turns out that I really don't. And I am not afraid of math, maybe I should have more respect for it though. I had a very long and confusing post about that not too long ago. Maybe it can be cleared up here too?

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    Member tjm's Avatar
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    I'm far from an expert but I've always thought that if you have 2 identical boats with the same pump and impeller, it doesnt matter if a gas motor, diesel motor, or gerbil is spinning the impeller you'll get identical performance at each rpm....assuming the gerbil weighs the same as the motor

    so if the chev 350 and fnm diesel are capable of spinning the same impeller you'll need to consider other aspects to make your decision, i.e. cost, longevity, efficiency, simplicity of repair, etc...

    either that or I'm wrong someone else will have to tell you which it is...
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    The engine performance is relative to the impeller it can turn. Each impeller requires a certain amount of power to turn at any given rpm. I think what T is saying is if both engines turn the same impeller, say a 2.7 or something, at the same rpm, the boat performance will be the same. The difference would lie in fuel economy, cost, weight, dealer support, etc....

    I am not sure what either engine pulls as far as impellers, but I thought the fnm 250 and the small block 350 turned the same impellers. I dont know what rpm though...
    09 River Wild, 3 stages, LS power

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    Price a new Yanmar diesel that has enough torque to keep 3,000 pounds (or more) on step and then think about the conversion. I bet you are looking at $30,000 just for the motor.
    I was thinking of converting my 25 foot Thunderjet to diesel, Yanmar connected to a 241. Would of ran about $50,000. Talked to some guys running the same motor I was interested in, in a similar sized boat. They reported about 1.5-1.7 mpg with the Yanmar when running fully loaded . However none of them were running loads as heavy as we do when doing the Yukon/Koyukuk trips.

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    [QUOTE=Daved;1184619]I think the cost is the biggest issue myself. Heating oil, road diesel and the like should burn fine and are readily available.

    I know the newer model diesel trucks aren't designed to run on heating oil (or at least they won't run very long if you use it) so i'm assuming the newer style marine engines won't like it either.

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    Quote Originally Posted by Daved View Post
    I think the cost is the biggest issue myself. Heating oil, road diesel and the like should burn fine and are readily available. Diesel motors are supposed to last much longer and that is good when you are taking it down the Yukon every year. I want to overload my boat, so I want as much push as I can reasonably get, speed is not as important to me as keeping a good load on step. My other alternative is to buy a new to me wider boat and then start over. I will be running into the same problems as I am on all my other boats, used gear that is being pushed to it's maximum. I really can't afford a new boat. My ideal would be a 70+" extra plus, 20 ft long with this diesel in it. Suspension seats and 6 foot top. Hey Glen, do you make such a beast?

    Daved,

    We do! One of the new boats we have been working on is an all new Xtra Plus (XP) boat.

    The Xtra Plus has featured a 3/16” bottom and a wide bow for EZ access on and off the beach.

    What we have done with the new model (We don’t have it on our website yet) is keep the 3/16” bottom and wide bow. We made the standard bottom 6’ with optional 7’.

    It will be available in lengths of 17', 20' and 23'.


    Sides are like the popular sport or AK XL, with a gunnel you can walk on.

    The new XP is available as an outboard jet, sportjet and Hamilton inboard jet (gasoline or diesel).

    The boats pictured here are both 20' and have the 440 option which is ¼”bottom with a 3/16” doubler between the motor rails, making .440 aluminum thickness.

    Glen


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    Default marine diesel vs gas for jet boat

    Good looking set of boats.
    Do I give my friends advice? Jesus, no. They wouldn't take advice from me. Nobody should take advice from me. I haven't got a clue about anything..

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    Wow. Like you read my mind. What is the deadrise?

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    after you go diesel you will never go back...

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