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Thread: Building Arabella (An Atkin Ingrid)

  1. #1296
    Join Date
    Sep 2002
    Location
    Sonoma County
    Posts
    1,142

    Default Re: Building Arabella (An Atkin Ingrid)

    Just question on engine sizing.. the Nanni N4-50 is rated at 36.8HP . Don't know if anyone has spoken to you, or you've read up on sizing the engine to the hull?

    I don't know the lines/ displacement of your hull, but you CAN put in too much engine. The hull shape, how easily it's driven at hull speed, displacement, prop diam, prop pitch and blade count and a few other variables all contribute to essentially a "fixed load" the engine will "see" given the speed you choose to cruise at. I got lectured on this from the Forum 10 years ago in repowering my 5 ton 26' full keeled Cutter. It's nothing like a planing hull where it's almost impossible to have too much horsepower.

    There's nothing like a good WoodenBoat Forum brow beating to make an impression on you....

    Anyhow, the long and short of it is if a diesel is oversized for the fixed load it will never get into the fat part of it's performance curve. It can unbelievably fail to run hot enough which has efficiency implications. An overloaded diesel will overheat and blow headgaskets like tissues.

    So.. you may have already been tanned and hided, or are simply replacing like-for-like in terms of the Perkins' ratings and this engine. If it's like-for-like, pull out the performance curves of both engines (Torque vs RPM) and make sure they overlap. I'll be they won't as the Kubota is a "modern high speed" diesel which means it turns at nearly 3000RPM.. i"m betting the Perkins stays under 1500.. but all this is just conjecture...

  2. #1297
    Join Date
    May 2012
    Location
    UK. Cornwall, Suffolk.
    Posts
    5,126

    Default Re: Building Arabella (An Atkin Ingrid)

    Arabella is 10 tonnes ballasted? Rule of thumb for sailing boat aux engines is 3 horse @shaft! Per tonne.

    Most manufacturers put fairy dust HP ratings on the plate, and in any case do not know gearbox losses at the time of writing it.



    I have been going backwards in a 'rule of thumb' rated horsepower sailing boat. With tired crew, getting dark, wind starting to screech, and only shipping lanes behind me. More HP is good sometimes, and will only need to save the boat once. Up to each to decide what fuel consumption and weight to put up with.

  3. #1298
    Join Date
    Mar 2011
    Location
    Mukilteo, WA
    Posts
    2,211

    Default Re: Building Arabella (An Atkin Ingrid)

    The Ingrid is about 25000 lb so 11-12 tons depending on your units. I have a 4-107 and feel that is just about right. I cruise at 1500-1800 rpm with plenty of reserve if needed.

    Its rated at 38 hp continuous, 45 max according to google. Take that with a grain of salt I'm sure.

  4. #1299
    Join Date
    May 2016
    Location
    Ottawa, Canada
    Posts
    249

    Default Re: Building Arabella (An Atkin Ingrid)

    I would say engine / transmission / prop selection is a bit of an iterative process. The prop diameter may limit everything else based on clearance, or you add blade area, or you have greater slip, or you change transmission ratio .......

    We ended up with a spread sheet based on Dave Gerr's propeller handbook to play around with the options.

  5. #1300
    Join Date
    Sep 2002
    Location
    Sonoma County
    Posts
    1,142

    Default Re: Building Arabella (An Atkin Ingrid)

    Quote Originally Posted by Mark0 View Post
    I would say engine / transmission / prop selection is a bit of an iterative process. The prop diameter may limit everything else based on clearance, or you add blade area, or you have greater slip, or you change transmission ratio .......

    We ended up with a spread sheet based on Dave Gerr's propeller handbook to play around with the options.
    I got away with only having to repitch my prop once with the repower (new Kubota based 26HP 3 cylinder, 1 liter, replacing an Albin AD-2, two cylinder, 20HP, 1 liter).

    The first "guess" was not bad (using above mentioned method) so we got pretty close.

    "Close" meant I could hit about 80% of Redline, but not quite.

    A minor adjustment a year later (for next haulout) and it was perfect. Engine could be spun to max RPMs when needed and noticed about 1/2 Knot increase averaging the with the tide and against the tide speeds.

  6. #1301
    Join Date
    Mar 2014
    Location
    Ronneby, Blekinge, Sweden
    Posts
    721

    Default Re: Building Arabella (An Atkin Ingrid)

    Quote Originally Posted by DeniseO30 View Post
    I'm sure I missed it if it was mentioned just wondering about the decision to have square rivets.
    I have never heard of, read or talked about using round shafted nails when riveting.

    /Mats
    Yes the avatar depicts me; yes I drew the comic boat pic, it's a joke on the pop song I'm Not a Robot by Marina and the Diamonds.
    Swedish Yourneyman of the Year 2019

  7. #1302
    Join Date
    Aug 2014
    Location
    Westchester, NY
    Posts
    201

    Default Re: Building Arabella (An Atkin Ingrid)

    Steve discusses round vs square rivets in one of the videos about rivets.
    My Goat Island Skiff Project Photos:
    https://www.flickr.com/photos/999065...7648295059621/

  8. #1303
    Join Date
    Jan 2000
    Location
    Portland, Maine
    Posts
    17,639

    Default Re: Building Arabella (An Atkin Ingrid)

    Congratulations to the Arabella Crew on reaching the 100,000 Subscriber mark on YouTube!

  9. #1304
    Join Date
    Mar 2014
    Location
    Ronneby, Blekinge, Sweden
    Posts
    721

    Default Re: Building Arabella (An Atkin Ingrid)

    Granby (lit. spruce village in swedish) seems to be of spitting distance from Amherst, where I spent a year as an exchange student 30 years ago.

    /Mats
    Yes the avatar depicts me; yes I drew the comic boat pic, it's a joke on the pop song I'm Not a Robot by Marina and the Diamonds.
    Swedish Yourneyman of the Year 2019

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