capability of a semi displacement 12m boat

Discussion in 'Stability' started by jago, Nov 16, 2011.

  1. jago
    Joined: Nov 2011
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    Location: canada

    jago Junior Member

    OK we have bought a 1988 12m prowler sundeck by cooper yacht twin 7.4 merc power rag tops it has been well cared for and it was the best fit for our family of 5 vs budget. we would like to do the loop and maybe some island hopping. now the boat was built for the north pacific coast and i have been told it is above average in seas and a quality build i sure hope so! she only has 2 100g tanks. so my hope is for some positive input about range ,speed,salt capability,make model or anything you may feel relevant. please be nice i am a total rookie. we were asked to re name her so we called her grace for it is only buy gods grace that we have this chance! i know its not a trawler or a sail boat but how far can we go with extra fuel.any specs on line anywhere. thank you:)
     
  2. eyschulman
    Joined: Jul 2011
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    eyschulman Senior Member

    You are wise to take stock of your boat. I know nothing about it. Just want to point out that in any long journey it is not the boat. Put your time into self education and then you will select wisely and manage better. I tell you this because if you have to ask the question you probably need the education. This is not to say that rediculous voyages by people with little knowlege in ill suited boats dont come off.
     
  3. jago
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    jago Junior Member

    thank you and yes i am trying to educate myself as much as is available but most will probably be on the fly for right now im just reading chapmans piloting. i hope to get some training in the spring when she goes back into the water.
     
  4. WestVanHan
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    WestVanHan Not a Senior Member

    They are very well built boats and quite capable....I'm assuming you are east coast-whereabouts are you?

    Many of them came with Cat diesels.

    Couple quick thoughts on consumption as I am in a rush right now-the slower you go the better the mpg and try to go with currents and tides.
     
  5. jago
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    jago Junior Member

    thank you the boat is in ontario canada it has only been in fresh water but engines are suppose to be salt ready.
     
  6. WestVanHan
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    WestVanHan Not a Senior Member

    jago I phoned a friend who had one like yours (no aft cabin) but sold it a few years ago.
    He told me that around 12 knots he was getting about 1 mpg..he couldn't remember at lower speeds but I'd guess around 7-8 knots you'd probably get 3 mpg or maybe more.

    If it's on plane at 12 knots the mpg likely wouldn't drop very much if you sped up and in fact there's a good chance you may get better mpg at a higher speed.

    So your 200 gal tanks may get you 500 miles+ going slow and watching tides and currents.

    My 50' with twin 635 Cummins gets 3 mpg at 7 knots and at 24 knots gets about 10% better mpg than at 14.

    However I know nothing of the loop or the islands there so I can't tell you.
    But I wouldn't hesitate to take it around Vancouver Island in the right season while keeping an eye on weather and waves.
     
  7. jago
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    jago Junior Member

    thanks. boy she is a thirsty girl. i wish i had twin diesel but we will make due this is our first boat and we are in no rush but it is good to know we can plane to shore if weather gets ugly! do you think she could make Cuba if we carry extra gas.
     
  8. Tad
    Joined: Mar 2002
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    Location: Flattop Islands

    Tad Boat Designer

    Prowler42.jpeg

    I think the image above is roughly what you have? Perhaps without the hardtop on the sundeck? Note a great deal of boat above waterline and very little below....This boat is not designed for heavy weather! In my (Naval Architect's) opinion this boat is a textbook case of unseaworthiness. Note the flat and shallow bottom, blunt bow, tiny rudders and props, and no keel at all. Also note the huge windows well forward (where they are vulnerable to waves coming over the bow), low freeboard at the bow, and engine room vents below the sheer in the hull side (easily flooded).

    As long as you can keep the speed up (at least 10-12 knots) this boat will be reasonably controllable and have adequate dynamic stability. In a big sea where you have to slow down she will make everybody sick with her fast rolling, plus wear you out trying to keep her pointed into the waves. The combination of tiny rudders, no keel (for directional stability), and very high windage will keep her out of control. Loose power and you are in real trouble.

    She will probably be fine for the inland cruising you want to do, but I would recommend no open water passages until you have far more experience and know the boat better.

    Below is what I would consider a reasonably capable semi-displacement boat. The Nelson 42'. Note the differences from the Prowler. Lower height above water, higher freeboard at the bow, finer and deeper bow, less beam and more depth to the hull, no flying bridge on top of the pilothouse, huge keel, deeper draft, engine vents in the house side well above the sheer, bigger rudders, and smaller windows set well aft of the bow......These are just some factors that affect seaworthiness.......

    nelson42mk2master.jpg

    42mkII_drawing_large.JPG
     
    Last edited: Nov 18, 2011
  9. jago
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    jago Junior Member

    thanks for your input.i will not take it lightly! ok so how can i improve her sea worthy ability.i was thinking in kind about the vent set up too. i have to make the best with what we have. and i will certainly get some experience before i try any salt or even lake crossing. i still thank god for her every day. and yes the picture is right but i think it is smaller than our grace maybe not think our nose is longer.
     
  10. Tad
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    Tad Boat Designer

    jago, your boat is what it is.....improvements in seaworthiness will be expensive or will destroy whatever value the vessel currently has. For instance you could cut the flying bridge off....but I doubt you want to do that.

    I think the biggest gains can be had with crew education, with this will come better understanding of your ship and her limitations. You need to be able to listen to weather forecasts and understand the implications. You need to understand route planing and how and when to alter the plan based on current and predicted weather. You need to understand when not to go out and what not to try. I see beginners all the time trying to anchor in high wind with too small an anchor and no scope, or trying to tie up on the wrong side of a dock in a crosswind.

    With your education will come understanding of the need to make sure your boat is ready for sea. Just yesterday I was reading of some folks that set off to sail 1500 miles of open ocean without strapping the ships batteries down. The boat was rolled in a huge wave and the batteries were all upside down in the bilge.......Preparation and maintenance of systems to improve reliability is vital. Things like crap in the fuel tanks can stop you dead in a big sea when they get stirred up and plug filters.

    Use the boat you have, learn from that, and then if you still want to set off on longer journeys, get a more capable ship.
     
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  11. jago
    Joined: Nov 2011
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    jago Junior Member

    Again thank you for your wise words. And your right I am a total rookie and education is our greatest nead.As for our grace her fly bridge is sparce for weight. the ragtops can come down to reduce hight and resistance. I realise my hull is what it is. But what about water balist extra fuel tanks re routing the vents would none or this help if I did get caught in weather. I will never have the funds to upgrade to a true ship. I am a retired journyman welder with 3 kids and a 19 year old daughter. So I am lucky to have grace as it is. I got her for a song So i will just have to learn her limits so i can stay well within them. I think the loop will be a good exp. to start.
     
  12. Tad
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    Tad Boat Designer

    The addition of ballast is not really (IMO) a good idea. First off the boat doesn't have the structure to handle it, and additional weight adds drag to an already inefficient (at moderate to lower speed) hull (burns more fuel). Increased weight brings the bow, windows, and vents closer to the water, increasing the chance of damage. And lowering the center of gravity will increase the rolling speed, making people seasick quicker..........

    Re-routing the engine air vents would be a major project to do correctly (adequate size with minimum restriction). There should be two inlets and two outlets, the outlets should have non-sparking blowers fitted. I don't know the layout of this boat but sometimes the ducts can be run up in the corners of the deckhouse......

    Typical weak spots in the structure are the windows and their frames, and the deckhouse. To beef this up will increase weight, with the same result as above. I would pay attention to simplifying systems, reducing the number of through hull fittings, and arrange redundant pumps including a big hand pump. A decent dinghy with reliable outboard and plenty of fuel is your "get home" propulsion....but you need to learn how to use it. Carry three anchors (at least) and a long beach line and learn how to use them.
     
  13. WestVanHan
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    WestVanHan Not a Senior Member

    All of the side intakes I have ever seen have been routed through channels and boxes so as air gets in and any water that may splash in will just run back out....dorades.

    Go check your intakes J
     
    Last edited: Nov 21, 2011
  14. jago
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    jago Junior Member

    thank you for your input. i will have to look once we are back on grace. one more saskachewan winter it was -25 yesterday. i realy welcome the info!
     

  15. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    Absolutely......the usual thing is a open topped box glassed in behind the hull side louvers......this does indeed keep a splash from directly entering the engine space but it will not stop solid water. The downflooding point is a few inches higher and inboard of the lower edge of the hull vent.....So the boat fills with a couple of degrees more heel.....This is no big safety factor at all......

    With most hulls the righting arm is increasing right up until the deck edge goes under water. With a hole in the side of the boat below this point (deck edge) downflooding starts before maximum righting moment is reached, for some boats this may be less than 30 degrees heel......The hull side vents are cheap and easy, they take nothing away from accommodation, but they are far from the wisest or safest solution......
     
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