Cummins Marine Diesel Repower Specialists Forums Boats & Repowers Repower 35 Henriques Pilothouse

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  • #28724

    RiggersandFinsBda
    Participant

    I have a 35 Maine Coaster pilothouse that I am considering downsizing the engine from a 420 to 370 Cummins

    Is this a reasonable possibility in theory.

    We use the boat for recreational fishing and don’t need a speed demon.

    Again this is a boat with a 4kw Onan genset, 300gallons of diesel max and 50 gallons of water if we were full.

    It is an 18000lb boat

    I need to repower but budget dictates and I’ve seen another similar boat a 34 Duffy commercial boat have a repower with a 370

Viewing 9 replies - 1 through 9 (of 9 total)
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  • #69174

    RiggersandFinsBda
    Participant

    UPDATE: Engine is out!!

    Good day All,

    This is a LOOONGGG overdue update:

    I’ve managed to get the engine out and will be replacing it with an (apple to apple) direct model replacement. 6CTA 8.3-M.2

    Upon removing the current engine and tranny, it has been revealed, as expected that the coupling may need replacing.

    What is currently on the tranny is from VULKAN p/n# 1KT4110104. Is this something that you supply at Seaboard or is there an apple to apple upgrade as it is obviously an older model tranny (IRM301p.2)

    #29036

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    From your answer to my post, I am not sure if you understood what points I was trying to make..

    May I ask where you are located?

    Can you post some good pics of the 8.3 as currently installed in you vessel so we all can get an idea what what you are dealing with? Maybe a “smaller” engine will allow better service accessibility and that is part of the underlying issue or issues? But regardless, these engine are far from “apples for apples” as to the cruise power vs. RPM curves..

    The above may help me & others here that want to help understand your concerns better & if you want some added good input to help…

    Tony

    1 user thanked author for this post.
    #29025

    RiggersandFinsBda
    Participant

    Making this assumption.

    Your 6CTA 8.3 will make 2600 RPM and you cruise at 2000 RPM making 12 ks,. And, the overall installation and the condition of you engine is decent

    For a good running 6BTA 5.9 370, installed properly and set up to make a solid 3100 RPM at WOT, the 370 would have to run at 2400-2500 RPM to make the same power you are using now to make 12K’s..

    That means a MAJOR prop down sizing or a gear ratio change.. Do you understand that?

    Also–If you are having issues keeping your 6CTA running right, I will guarantee you the 370 Diamond will be more finicky that way..

    Where did you come up with suggesting that a 370 Diamond will cost less money to maintain?

    Also–Understand this–The 370 Diamond is actually 355 BHP the minimum 3000 rated rpm–Your current engine is rated at 420 BHP at 2600 rpm (minimum).

    These two engines are very far from “Apples for Apples”” and must be looked at that way.

    Nothing wrong with what you want to do, but you need to understand the “engineering part” of what these engine can do, but more important, what they cannot do.

    Tony

    To be clear the issue isn’t keeping the 420 running right. The issue is the maintenance required on this particular engine versus dropping a new engine pricewise arent close.

    We need aftercooler service. Turbo service. Cylinder work. New Seamax water pump amongst other things.

    These things at local prices are outrageous.

    A reconditioned 370 is cheaper if you add shipping duty and freight.

    I will give you an example or two:

    New 420 installed quoted at nearly 70k.

    New lift pump (from same local dealer) quoted at nearly 600 dollars *before* installation.

    Same lift pump purchased by me cost less than 200 from east coast Cummins dealer and installed by me and a friend.

    I know a guy has to make a living but the guy wants almost twice as much as a new engine to do it all…….

    #28776

    Rob Schepis
    Forum Moderator
    Vessel Name: Tenacious
    Engines: 6BTA 5.9 330's - "Seaboard Style"
    Location: Long Island, NY
    Country: USA

    Here’s the performance curves for both. Just compare and you will see what the 370B needs to turn to match the output of the 420C. I’d rather loaf a C than push a B…

    #28762

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    Making this assumption.

    Your 6CTA 8.3 will make 2600 RPM and you cruise at 2000 RPM making 12 ks,. And, the overall installation and the condition of you engine is decent

    For a good running 6BTA 5.9 370, installed properly and set up to make a solid 3100 RPM at WOT, the 370 would have to run at 2400-2500 RPM to make the same power you are using now to make 12K’s..

    That means a MAJOR prop down sizing or a gear ratio change.. Do you understand that?

    Also–If you are having issues keeping your 6CTA running right, I will guarantee you the 370 Diamond will be more finicky that way..

    Where did you come up with suggesting that a 370 Diamond will cost less money to maintain?

    Also–Understand this–The 370 Diamond is actually 355 BHP the minimum 3000 rated rpm–Your current engine is rated at 420 BHP at 2600 rpm (minimum).

    These two engines are very far from “Apples for Apples”” and must be looked at that way.

    Nothing wrong with what you want to do, but you need to understand the “engineering part” of what these engine can do, but more important, what they cannot do.

    Tony

    #28750

    RiggersandFinsBda
    Participant

    2000 rpm cruise 12kts
    2600 rpm WOT 16.5kts

    Based on current condition

    #28738

    Rob Schepis
    Forum Moderator
    Vessel Name: Tenacious
    Engines: 6BTA 5.9 330's - "Seaboard Style"
    Location: Long Island, NY
    Country: USA

    What WOT rpm is she propped to now?
    What rpm is required to make the 12knots out to the grounds and then what rpms to make it home at that decent hour?

    #28735

    RiggersandFinsBda
    Participant

    We have a Cummins 6cta 8.3m2.

    It is a good engine but needs quite a bit of TLC that locally is cost prohibitive to do.

    We can get a good 370 for a good price shipped and more than likely installed for a fraction of what a 420 would run us.

    A typical day of fishing is 10 to 12 knots to the fishing grounds @ 1.5 hours travel; 4 to 8 knots trolling @ 4 to 5 hours and then back home at 8 to 10 knots for an hour before pushing the throttle up to get home at a decent hour.

    #28729

    Rob Schepis
    Forum Moderator
    Vessel Name: Tenacious
    Engines: 6BTA 5.9 330's - "Seaboard Style"
    Location: Long Island, NY
    Country: USA

    Is it mostly at hull speed and trolling? When you do need to get up and go at what HP are you happy with your current engine. What is the current engine exact model? Is that 420 the Yanmar 6LY or the Cummins 6CTA or ??

Viewing 9 replies - 1 through 9 (of 9 total)

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