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Thread: 8m Engine Upgrade

  1. #1
    Join Date
    Dec 2017
    Location
    Cornwall
    Posts
    11

    Default 8m Engine Upgrade

    Hi,

    I've now got a Catalac 8m with twin 10hp Yanmar (shafts). I've found in some conditions I struggle to manage more than about 2 knots (on engine alone). If I wished to upgrade the engines to a 20hp pair, is there a suitable engine that others have chosen before?

    Linus

  2. #2
    Join Date
    Oct 2008
    Location
    Worcester, U.K., Moraira, Spain
    Posts
    561

    Default Re: 8m Engine Upgrade

    Not specifically Catalac related but I know a couple of people who've replaced Yanmars and Volvos with Beta Marine. They do a 20hp but as it's 3 cylinder it might be physically a bit big. They have a 16hp that is 2 cylinder so might be a better bet. http://betamarine.co.uk/portfolio-item/beta-16/

  3. #3
    Join Date
    Dec 2017
    Location
    Cornwall
    Posts
    11

    Default Re: 8m Engine Upgrade

    How concerned should I be about extra weight?

  4. #4

    Default Re: 8m Engine Upgrade

    Quote Originally Posted by uklinus View Post
    Hi,

    I've now got a Catalac 8m with twin 10hp Yanmar (shafts). I've found in some conditions I struggle to manage more than about 2 knots (on engine alone). If I wished to upgrade the engines to a 20hp pair, is there a suitable engine that others have chosen before?

    Linus
    Are you happy with the propellers? I'd check on sizing and pitch of those first, a lot cheaper than an engine change(s). Chances are if you change the engines you will also need to change the props.

  5. #5
    Join Date
    Feb 2009
    Location
    Belgium
    Posts
    374

    Default Re: 8m Engine Upgrade

    Quote Originally Posted by uklinus View Post
    I've now got a Catalac 8m with twin 10hp Yanmar (shafts). I've found in some conditions I struggle to manage more than about 2 knots (on engine alone).
    Linus
    Hi Linus, I suppose that is 2 knots SOG, what currents/headwind are you fighting against?

    Quote Originally Posted by Peter View Post
    Are you happy with the propellers? I'd check on sizing and pitch of those first, a lot cheaper than an engine change(s). Chances are if you change the engines you will also need to change the props.
    I second that, 2 twin Yanmar (in good condition) should be sufficient for the 8M. Props are very, very important so indeed you will need to check if they are the right size/pitch for the 8M (can't help, have an outboard, installed new by the previous owner, also in need of a better prop but this is common on outboards if they are not 'high thrust' versions)...

    I suppose you have a clean hull (not fouled heavily I mean)...
    Any idea how heavy you are loaded now? Full cruising gear? As yes, weight impacts performance, especially aft...
    1979 Catalac 8M - 8-84 - Galu'Lati Go

  6. #6
    Join Date
    Dec 2017
    Location
    Cornwall
    Posts
    11

    Default Re: 8m Engine Upgrade

    Quote Originally Posted by djeeke View Post
    I second that, 2 twin Yanmar (in good condition) should be sufficient for the 8M. Props are very, very important so indeed you will need to check if they are the right size/pitch for the 8M (can't help, have an outboard, installed new by the previous owner, also in need of a better prop but this is common on outboards if they are not 'high thrust' versions)...

    I suppose you have a clean hull (not fouled heavily I mean)...
    Well, since writing this I have done some investigation, and one of the engines is suffering significant loss of compression and so that is clearly not helping at all, so will be getting the head off and sorted over the next week or two. Also, I've noticed the folding props are not actually folding, so I'm not sure if they might be fouled so the next investigation will be to find somewhere I can let the boat sit whilst the tide runs away so I can see whats going on down there. Hopefully I'll get to the bottom of this!

    Quote Originally Posted by djeeke View Post
    Any idea how heavy you are loaded now? Full cruising gear? As yes, weight impacts performance, especially aft...
    Not at all heavy at the moment, only minimal stuff on board.

  7. #7

    Default Re: 8m Engine Upgrade

    Hi uklinus,

    engine trouble is a headache and usually a guaranteed source of income for dealers.
    My experience with (refurbished by me) original 1 GM engines is getting 4-5 knots on a single engine, 5-6 on both engines.

    Beta does have drop-in replacement engines (2 cylinders, a welcome change from one lunger bangers, also hot water connection).

    You can go for more power, but you will have to adapt the engine mounting brackets and accept more weight on the stern...!

    All the best,

    Puck
    Last edited by Puck; 10th June 2018 at 06:54 PM.

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