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Thread: Marine Diesel Engine Preferences

  1. #1

    Default Marine Diesel Engine Preferences

    We are looking into a new boat that would have twin diesel engines.
    We've always had boat with outboards up until now. My knowledge of marine diesel engines is limited. Would greatly appreciate any discussion/recommendations regarding the myriad of marine diesel engines out on the market.
    Size of boat...~36' x 14'.

    Much Thanks in advance.

    Jim

  2. #2
    Sponsor potbuilder's Avatar
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    Shaft or outdrives ??

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    Ask the same question on the Hull Truth forum.

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    Member jaydog's Avatar
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    Default

    boatdiesel.com is a great resource.

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    Member jrogers's Avatar
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    What is your home port? What motors does your local mechanic know well? This is one of the biggest factors.

    Sent from my SAMSUNG-SGH-I727 using Tapatalk 4
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  6. #6

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    Outdrives..

    Quote Originally Posted by potbuilder View Post
    Shaft or outdrives ??

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    outdrives hand over face.jpggood luck keeping any drive together with a boat that size !! Whats in the boat you are looking at ?? There's not much on the market that will last long on a boat that size. If you want diesels then look for a boat with shafts and transmissions. Now all the guys with the newer volvo's with drives will tell you they have 500-1000 hours of trouble free use with their diesels, see what they say after 5000 hours ??? Oh by the way have i told you all outdrives are junk !!! i know i had them for 20 years on my bowpicker, never ever again !!!

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    Great info Steve. The builder is pushing stern drives VERY hard.

    Assuming we stayed with good ole shafts/transmissions is there a brand of marine diesels that fare well in AK?
    As previously mentioned by others service, parts, etc... are very important. I'm looking for general guidance re the engines similar to your advice re stern drives. The advice is much appreciated!

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    Quote Originally Posted by Jrddiver View Post
    Great info Steve. The builder is pushing stern drives VERY hard.

    Assuming we stayed with good ole shafts/transmissions is there a brand of marine diesels that fare well in AK?
    As previously mentioned by others service, parts, etc... are very important. I'm looking for general guidance re the engines similar to your advice re stern drives. The advice is much appreciated!
    They all want to install outdrives because its easy for them but hell on the owner. If it were me i'd look at cummins, john deere, iveco or cat and twin disc or ZF are both good gears. You haven't mentioned where you'll be docking the boat and that might help choose which power due to available service/support. Call me if you need more info. By the way there are some real deals nice boats back east to be had, i'm talking real boats not the go fast(nice weather) boats they push here but real comfortable boats.

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  10. #10

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    Potbuilder,

    8.3 Cummins, twins... Now talking about surface drives for propulsion. What do you think??

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    Quote Originally Posted by Jrddiver View Post
    Potbuilder,

    8.3 Cummins, twins... Now talking about surface drives for propulsion. What do you think??
    Cummins are great motors. Surface drives worse than outdrives, i saw a couple of bowpickers with them in cordova none preformed well. Did i see on THT that you are getting a cat hull ? Seems like a lot of horsepower needed to make it go ?? I thought those hulls pushed easy ?

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    Family's new boat is a 22,000 lb (or 24,000 I forget) 36'x12' twin 200hp volvo turbos straight shaft driven. 17 knots at 3,000rpms cruise 1.0 nmpg. Tops out a 24 knots at 3900 rpms. 2,500 hours on the motors.

    I wouldn't want to feed it gas for 3-4 outboards.

    Sobie2

  13. #13

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    Quote Originally Posted by potbuilder View Post
    Cummins are great motors. Surface drives worse than outdrives, i saw a couple of bowpickers with them in cordova none preformed well. Did i see on THT that you are getting a cat hull ? Seems like a lot of horsepower needed to make it go ?? I thought those hulls pushed easy ?
    The thinking w the bigger engines is: bigger engines = less rpm's for a specific speed = longer life on the diesel engine.
    Smaller engine = higher rpm's for specific speed = less engine life on the diesels.

    Steve, they're still recommending the surface drives...my question posed to them is "who up here will fix em' if they go down? Any ideas??

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    Quote Originally Posted by Jrddiver View Post
    The thinking w the bigger engines is: bigger engines = less rpm's for a specific speed = longer life on the diesel engine.
    Smaller engine = higher rpm's for specific speed = less engine life on the diesels.

    Steve, they're still recommending the surface drives...my question posed to them is "who up here will fix em' if they go down? Any ideas??
    I have no idea who would work on them? ?? Isn't it the builders responsibily to at least have a clue on where service is available for something they are installing on their boats. There is no way i'd stick those surface drives on a boat of mine! ! If they keep insisting on installing them i'd go look for another builder.

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    Member Sobie2's Avatar
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    Ok Jrddiver,

    Who is the builder you are talking to? There are a lot of Arneson driven boats made in BC, but no where else really. Also unless you are running a 1:1 ratio your prop turns more RPMs per engine revolution the faster you go. A diesel engine manufacturer will tell you what the duty rating is for each engine. There are also different ratings (heavy duty, continuous duty etc). There re diesels out there where the duty rating is only 200 rpms less than the redline. At the dutry rating your engine is designed to run there for ever. For outboards (for example) the industry standard is 80% of the top rated RPM of the engine. Diesels can be much closer to redline than that and live forever.

    Here is what you have told us:
    8.3 Cummins (twins) 36' x 14'

    Here is what you haven't told us: ARMSTRONG CAT
    Fiberglass, aluminum?: ALU
    Approx Weight? 24,000 lbs
    PotBuilder says you may have indicated a Cat (vs mono) on another forum: CAT
    We are guessing planing vs displacement (but some Cats are semi displacement): PLANING
    Desired cruise speed. HIGH 20s cruise TOP speed mid 30s
    What HP/model of 8.3 Cummins?

    Snooping in THT revealed the info... So now knowing more, Armstrong has built 2 whale watch boats for the Juneau Market. Both are big, one has 2 Yamaha F350 V8s, and the larger one has 4 Yamaha F300 V6s. There is definately a price point for outboards vs diesels. But on a boat like this price isn't that big a factor (lets be honest here if you are having a boat made $ isn't a real factor Armstrong has built many Cats for Alaskans (a number for the Juneau market where I am). There are Volvo I/O diesels, Yamaha outboards, no surface drives come to think of it, I am curious about this one (perhaps they have a pair lying around the shop that need a home, doubtful as Amrstrong is an ethical company).

    Sobie2

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    Member jrogers's Avatar
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    Here is a thread with a lot of baseless opinions on Surface Drives and some real world experience mixed in:

    http://www.thehulltruth.com/boating-...ce-drives.html
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  17. #17

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    There's a guy in Valdez that repowered his CAT with surface drives from sterndrives. Wasn't a very successful transition. Consumed way more fuel, load, and could see him coming from miles away for the roaster tail the throw.

    36' is allot of boat to push. Have you considered using jets.

  18. #18

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    My original plan for the boat was outboard Yami's, but Johnny at Armstrong insists the boat is too big for twin 350's.
    They are not recommending stern drives because they "fall apart" after 500 hrs on a boat like this (his words not mine). They are very high on the surface drives....and I can't figure out why. I am not, but this has quickly risen above my pay grade in the world of boat propulsion, hence, my constant banter on this forum and PM with a number of participants. I have asked Armstrong directly who would they have service these drives up here in AK. I'll let you know there response when I get it.

    Jets are an option.

  19. #19

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    Sobie2

    Can you clear your PM space so you can accept new PM's.
    Tried to send you one, but your PM box is full.

  20. #20

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    Steve,

    Here's what we'll be putting on the Armstrong.
    Check out the web site.

    http://www.seven-marine.com/motors/p...nd-technology/

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