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Thread: McThirsty

  1. #1

    Default McThirsty

    Just installed a Flowscan in customers boat with a new 8.1L coupled to Hami HJ212 with 4.0T. I've heard they were thristy but didn't realize how much they like the fuel.

    Check out the videos.

    For comparison, The FNM HPE300 we installed in a Phantom Avenger with the 4.0T showed only 5.5gph at 2900rpm. 10.5gph@3400 and 17gph at 3800.

    At idle the 8.1 was consuming 3gph. a 300hp diesel comsumes less the .5gph The 8.1 consumes 6gph at 1500rpm.

    We weighed an 8.1 fully dressed with oil recently and it weigh 1050lbs. The 300 diesel weighs only 720lb.

    There's some serious savings to be had with the diesel not only in fuel but in weight.

    Cheers







  2. #2

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    Scary....

    I watched in fascination (horror?) over a span of weeks on one web site where a guy was fighting to improve mileage on his 26' boat with twin 250's. He got it to 28GPH for 25mph, and guys were patting him on the back.

  3. #3

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    Interesting for sure. Before GM stopped making the 8.1 you could find them new in the crate on Ebay for anywhere from $7,000-$8,000. What is the price for the FNM HPE300 ?

  4. #4

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    Those numbers don't scare me much...we are burning 12gph at idle (diesel), 20gph @ 10mph, and escalates to over 160gph at speed. The generator burns a gallon an hour too!

    The other boat (28') with a 8.1 cruises at 30mph consuming 1.3mpg. I'm guessing that there is a pretty big difference in the 300 horse diesel and the 375 horse 8.1...especially in throttle response and max rpm.


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  5. #5
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    I got a 8.1 in my 24' Seasport. It Burns 9 gph at 18 knots, 11 gph at 26 knots and 15 at 30. Full throttle is a little scary, it buries the needle somewher over 32 gph and 40 knots, but cruising seems about the same as ive heard from other motor setups on similar size boats.
    I think my prop is one size to small, I overrev at full throttle, but I doubt It would make enough improvement to justify the 1500 for a new stainless douprop set.

    Sent from my SAMSUNG-SGH-I777 using Tapatalk 2

  6. #6

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    Quote Originally Posted by AK2AZ View Post
    Those numbers don't scare me much...we are burning 12gph at idle (diesel), 20gph @ 10mph, and escalates to over 160gph at speed. The generator burns a gallon an hour too!

    The other boat (28') with a 8.1 cruises at 30mph consuming 1.3mpg. I'm guessing that there is a pretty big difference in the 300 horse diesel and the 375 horse 8.1...especially in throttle response and max rpm.
    What kind of diesel boat you running to be burning 12gph at idle??? The Chenega??

    30mph at 1.3mph is 23gph. Ouch!

    As for throttle response theres not much if any difference. Side by side out of the hole had only a slight lead with an 8.1. At cruise speeds to WOT the diesel actually pulls away for the 8.1 but the 8.1 is faster at WOT. The boat in the video has the 8.1HO motor, 425hp and turned the 4.0 to 4100. A Standard 8.1 with a fresh rebuild turned the 4.0 to 3900rpm. The diesel turns the 4.0 to 3800. I assume fewer rpms are made up with the nearly 400lbs in less weight over the 8.1.

  7. #7

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    Need to know the price of the motor otherwise it is useless to try to compare anything.

  8. #8
    Member mainer_in_ak's Avatar
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    holy smokes, that fuel consumption is insane with either boat. My last hunt, 374 water miles (gps was always on) with both a moose and a caribou, I burnt 28 gallons of gas. I was pssing and moaning about that. I'll stop complaining now.

    Last run: 70 salmon/6 hrs of boating on kenai, two men, we burnt 2.75 gallons of gas. that's 3/4 gallon more than last year when I wasn't trying to fill two permits.

  9. #9

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    those canoes are very efficient . . .

  10. #10
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    I have a hard time believing the fuel use for an 8.1 at idle? I have an 8.1 HO, Hami 212 with a 4.0 in a 24' boat and I get 10-14 GPH depending on load and RPM, The weight it will haul and reliability of this combo is amazing. I am sure the diesel is a good motor, But the cost of diesel fuel and the intial cost of the engine gotta factor in there some where? I havent seen any bigger boats with on board diesels yet?

  11. #11
    Member Bob the fisher's Avatar
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    Ok, while we are talkin about it, the saltwater boat I'm on is a 30' Glacier Craft. Fully loaded, it weighs in at just over 15,000 pounds. Its powered by twin 250 Yamys with stainless props and on flat calm seas it cruises at 32 mph burning 28 gph. I don't think that is too bad for that big of a boat. Is it?
    "Fisherman for Life" and "Phantom owner Forever"

  12. #12
    Member DownEastah's Avatar
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    I had my 22 seasport with 6 people and a dog and 200 lbs of fish cruising at 27 mph and burning 10-12 GPh Normal load me and my wife and dog I cruise at 28 burning 8 GPH. This is with a 175 Suzuki

  13. #13
    Moderator bkmail's Avatar
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    My 502 BBC airboat burns 1 mpg on ground and 2-3 mpg on water depending on depth and load.
    It hauls 2000 lbs though without breaking a sweat across tundra and brush. The boat weighs 4500 lbs.
    AND WE LOVE IT!
    BK

  14. #14

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    Quote Originally Posted by Halibutgrove View Post
    What kind of diesel boat you running to be burning 12gph at idle??? The Chenega??

    30mph at 1.3mph is 23gph. Ouch!

    As for throttle response theres not much if any difference. Side by side out of the hole had only a slight lead with an 8.1. At cruise speeds to WOT the diesel actually pulls away for the 8.1 but the 8.1 is faster at WOT. The boat in the video has the 8.1HO motor, 425hp and turned the 4.0 to 4100. A Standard 8.1 with a fresh rebuild turned the 4.0 to 3900rpm. The diesel turns the 4.0 to 3800. I assume fewer rpms are made up with the nearly 400lbs in less weight over the 8.1.
    The big burner is a 58' Viking with Man Marine diesels...a pair of V12s each running twin turbos. While it is not fuel efficient it is fast at 45 knots considering it is 90,000 lbs. The other is a Bayliner 2859.


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  15. #15
    Member coho slayer's Avatar
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    So, does the diesel match up in regards to speed, time to get on step, etc? Not sure telling us what it burns at certain RPM's is telling the whole story. EDIT: I missed post #6, which answers some of the questions.

    And the lack of response to initial cost of the diesel is ominous.....

  16. #16
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    That and considering who started the post. Sorry it had to be said. In my defense I love laying down some serious black smoke with the truck, and think it would be cool in the boat, but there are lots of unanswered q's!

    Quote Originally Posted by coho slayer View Post
    So, does the diesel match up in regards to speed, time to get on step, etc? Not sure telling us what it burns at certain RPM's is telling the whole story. EDIT: I missed post #6, which answers some of the questions.

    And the lack of response to initial cost of the diesel is ominous.....

  17. #17

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    My 31' Charter boat burns 20gph going 26kts.. fully loaded. (7 guys) Twin 250 Verados

  18. #18

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    Quote Originally Posted by coho slayer View Post
    So, does the diesel match up in regards to speed, time to get on step, etc? Not sure telling us what it burns at certain RPM's is telling the whole story. EDIT: I missed post #6, which answers some of the questions.

    And the lack of response to initial cost of the diesel is ominous.....
    Coho, haven't really had time to post but yes time to get on step is nearly identical. I've done a couple side by side runs with the 250 and hamilton against others in the past and even with 90 gallons on board and 5 passengers I stayed with a 350 out of the hole and they only pulled away on the top end. The other boat was light on fuel and only had 2 passengers on board. Ran side by side with a bigger boat with an 8.1. and pulled head of him by 4-5 boat length before he caught up to us.

    As for cost. A new HPE250 runs $19,500 and a 300 will set you back $25,500 if a guy was going to just do a repower. When a boat is purchased new with a diesel you save allot more money and the diesel option adds about $10,000 to the overall cost. To some, 10K may seem like breaking the bank but that adds about $1200 to the annual payment over a 10yr loan. Based on what we saw with the 8.1 at 2900rpm it was burning 14gph. A 300 Diesel at those rpm burns 6-7. Burning an extra 6gph, a guy would use 600 gallons over 100hrs and spend $2400 extra he'll never get back.

    Going diesel isn't for everyone, but for the guy who puts lots of hours on his boat, wants an extended range, wants the safety of diesel over gas along with nearly equal performance its well worth the extra cost. Properly maintained and operated the engine should last the life of the boat.

  19. #19
    Member coho slayer's Avatar
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    Thanks! It is a hit on the price, but like you said, it could easily be worth it in the long run.

  20. #20
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    The reality is this: You have to burn a lot (per hour) before it makes sense for the upcharge. But it makes sense for many people who do use it enough (or have to pay enough per gallon for it to make sense). If you use your boat 100 hours a year it may be questionable.... If you put 500 hrs on a year definately. The payoff changes as fuel prices change too, and the long term projections are only going up for fuel... think about 15 years from now. That diesel will still be running. I just was in Iceland at the beginning of July and paid the equivalent of $120 to fill up a tiny VW Polo (smaller than a Golf) that was like $8.00 a gallon!


    Most big boats get 1-2 nmpg. Anything that increases that (like going diesel) is a major imporvement going from 1 nmpg to 1.2 nmpg is a 20% increase in fuel economy and when you have a 150 gallon tank or larger that pay off is quicker.

    In the end repowering a boat is a hard call to make, buying new is really the time to go with diesel. We have hundreds of threads on outdoorsdirectory on repowering and the decisions.

    Lastly I think a big selling point on the plus side of diesel is this ethanol thing. I am having a lot of issues with all of my outboards lately (past few years) with ethanol and dirty/rusted/water in the carbs. It really is worst in smaller outboards. With diesel you skip all that, and when in remote AK that only compounds things worse regarding reliability. Come think of it you can grow your own diesel in AK, and you can use fish oil in a diesel too.

    Lots to ponder.

    Sobie2

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