Looking for efficient low HP, need opinions!

Discussion in 'Boat Design' started by Wavewacker, Jun 21, 2016.

  1. Wavewacker
    Joined: Aug 2010
    Posts: 696
    Likes: 21, Points: 18, Legacy Rep: 226
    Location: Springfield, Mo.

    Wavewacker Senior Member

    This will only be used on rivers, inlets, lakes and not offshore cruising. It's the camper cruiser I've talked about several times.

    My goal is 10 hp, cruise at 10 maybe to 15 k, which requires a long and narrow boat. Another option is a 55lb thrust trolling motor with a battery bank and charger/genset.

    I'm liking the Key Largo here;

    http://spirainternational.com/study/KeyLargoStudy.pdf

    I understand it may be less in beam to get there.
     
  2. nzboy
    Joined: Apr 2011
    Posts: 154
    Likes: 4, Points: 18, Legacy Rep: 36
    Location: nz

    nzboy Senior Member

    I think if 10 hp limitation is a must ,10-15 knots is a pipe dream in a 7metre boat even if you reduced the beam it still would not get over 10 knots also the hp delivered to propeller on a sustained voyage is probably only 6hp which might make 7 knots .So what is needed is 35hp motor that is just idling along at 7 knots but has a bit extra to go faster .Spira designs are quite nice and achievable for the amateur
     
  3. Rurudyne
    Joined: Mar 2014
    Posts: 1,130
    Likes: 29, Points: 48, Legacy Rep: 155
    Location: North Texas

    Rurudyne Senior Member

    You might consider a scale up/stretch of something like John Atkin's Happy Clam (it's how to build can also be found online and is free) which at 17' attained nearly 15 MPH on plane with a 5 HP engine, loading not specified.

    Just going by the increase in displacement, a scale up of 25% (double the displacement, useful for carrying more gear) should roughly meet your speed and power requirements, be of similar length to the boat you linked to, and would also come with a relatively easy to beach form.
     
    1 person likes this.
  4. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 239, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    You could also take a look at Lathrop's Bluejacket 24: http://bluejacketboats.com/boats/bluejacket-24/
    with 50 HP it makes 24 mph (21 kt), so with 10 HP it should be able to deliver the speed you need - depending on how much stuff you put on board.
     
  5. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 470, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    With 10 HP you can easily get a light clamming skiff or similar, into low plane mode. With 55 pound trolling motor (about 2/3's of a single HP) you're never going to see anything other than displacement speeds. My Digger 17 design (17' LOD, 15' LWL, 6 beam) will reach the high teens (about 17 - 18 MPH) with a 10 HP engine and a light load (700 - 800 pounds) and it's not an especially light design. A light version of this would bust into the low 20's with a 10 HP outboard.

    Small camp cruisers fall into two basic categories; too small to have onboard accommodations, but enough storage to make an on deck or shoreside conversion into camp accommodations or the second; a micro, which has minimalistic accommodations and storage.

    A tripper canoe (as an example) would be in the first category, while there are several box boats (and others) types of micros that seem to fill the second.

    Will you camp aboard or be beached? Distances you expect to travel in a weekend? Crew, equipment, etc.?

    Rescue Minor comes to mind, as do several Atkins boats, but I think you can go more modern if desired, with several offerings from living designers.
     
    1 person likes this.
  6. nzboy
    Joined: Apr 2011
    Posts: 154
    Likes: 4, Points: 18, Legacy Rep: 36
    Location: nz

    nzboy Senior Member

    I don't know whether it would be comfortable doing the loop in a 17 foot dory open or enclosed .You were looking at the spira boat but if had a choice Id go
    for Pauls cooper design ,a very attractive boat for a small live aboard you are getting attractive plans for a cabin rather than putting your own box on an open boat put on a 20hp outboard
    RYD-22'11wSM.jpg
     
    1 person likes this.
  7. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 470, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    50 HP is the smallest I'd recommend for Cooper Jr. and this would just get her into the mid to upper teens, on a modest load. Generally, I recommend 70 HP or more on this design. This isn't what I'd consider the efficient low power design the OP was looking for either.
     
  8. Wavewacker
    Joined: Aug 2010
    Posts: 696
    Likes: 21, Points: 18, Legacy Rep: 226
    Location: Springfield, Mo.

    Wavewacker Senior Member

    Thank you everyone!

    NZboy, good memory, as I have posted about doing the Loop, however this boat isn't really intended to do the Great Loop. My conclusion of a "Looper" is to buy a boat, about 32 feet for the loop as that will require us to liveaboard about 3 1/2 months or more.

    Daiquiri, I like the Bluejacket, it's a sharp looking boat. I should have been more clear as to the SOR, a cabin or enclosure, hopefully with standing headroom.

    Rurudyne, yes, Atkins has several boats that would be fine and 21 ft may be just the thing, I'm thinking 24 ft. should be the maximum length I should bite off on a build.

    PAR, I really appreciate your input and I don't like long posts as I feel like folks lose interest and they often don't really read boring chatter. The purpose of this boat is much different than others I've discussed before, a bit of reality has set in!

    The Key Largo I posted has an interesting story to it, it was designed for some war torn villagers who had their boats destroyed and left to starve taking away their ability to fish offshore.

    I've never had a dory, but I'm learning they are a very old proven design and very capable in rough waters. They can carry a considerable load and can get into the shallows. While they can get up and dance, I'm simply looking for a decent cruising speed with a fuel burn rate of 1 or so gallon per hour, 1.5 is acceptable.

    More to the SOR or wish list.

    The use; Mainly the lakes of Missouri and Arkansas, Lake of the Ozarks is the largest, but we would like to cruise major rivers, the Mississippi, Mo. Ar. Tn. Oh. Buffalo and the White River, yes many of these are on the Great Loop.

    Not sure we'd get there, but the Gulf and Keys would be great. I don't know but for safety I may need more HP! Might go to 25 hp, but the burn rate is an economic issue. There is no expectation of planning on a trolling motor.

    Souls on board; 2 of us with our Boxer, but it would be nice for up to 4, maybe 6 for a day cruise or just a short run on a lake.

    Need a double or V berth and about 3' for the dog, she curls up on the floor.

    Ice chest or small fridge, camp stove (propane) and a porta-pottie with privacy. All under cover or in a cabin, thinking like the birdwatcher or Bolger's river cruisers. Would really like a trawler style cabin. A high hard top with canvas would be great too.

    Need standing headroom at least to stretch, I do cruise in the winter, New Year's Day is a ritual.

    Only need about 6' of cockpit, that's enough for 2 to sit out and throw a line. I really like the idea of a center cockpit that could carry canvas for overnight. An aft cabin with rails would be a good place for others to sit or for the dog. A slight arched aft top would work for any dog emergencies :) One of the Key Largo pictures shows a high hard top, put zip in sides on that and that would be nice too.

    I'd like to keep the beam under 8', 6' would be fine. I think all of this can fit in 20 to 24 feet.

    Now, the hard part, self righting and self bailing (well as much as possible) Heavy stuff down low, flotation inside and top. Easy boarding as well.

    Cargo; provisions and gear can be under 800 pounds, certainly under 1,000 pounds, that includes a generator and water. Not fuel.

    Range; as far as I can get, we may cruise for up to 10 hours a day, 75/80 to 100 miles, 3 to 4 days out on large rivers. That sounds like 300 miles, and about 30 to 40 gallons of gas.

    Obviously this goes on a trailer. Here's a contradiction, heavily built but light! LOL I want at least 3/4 inch bottom, I'm going to beach it and hit ground, I'd feel better with an inch of ply.

    This is to be a lumberyard boat, glass tape, epoxy and paint, I don't want to fiberglass the whole boat. Ply on frame, I feel comfortable with that. I don't want to spend 2 years working on it, build time within 3 or 4 months. A dory or a garvey (a runner up) of this size can be knocked out in 5 weeks I'm sure, but this is my first build. Let's say build time under 1500 hours for a newbie. Work boat finish.

    I have common hand and power tools, not a woodworking shop. I can build off the garage floor/horses and/or a strongback.

    I have some treated 4x6 posts 18 feet long, several and a couple 6x6 posts along with common lumber, hope I can use it.

    Personal; I'm experienced at 65 with power boats on lakes and rivers, not the Great Lakes or offshore. I was athletic and an Army Officer, but frankly age is setting in, I have some back issues and I'd say my 50 year old GF is in good shape, she can out work me! I'm still a strong swimmer, but she doesn't really swim, but the dog can :)

    Hopefully I covered the bases.

    Thank you again!

    Bill
     
  9. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 470, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Once reality sets in on a design search Bill, the posts naturally get long. My verbosity has bored many here I'm sure, though it's usually just trying to be accurate, inclusive or fair. Even a simple SOR can get quite involved, unless it's a 16' day boat.

    The dory has a reputation that is well misunderstood and overrated in today's reality. As sea boats they suck, unless it's a traditional dory, with a half a ton of cod in it's belly and a several scared sailors, are wrestling it back to shore in a gale. What's being called a dory today isn't one of these, but a dory looking thing that has been lightened considerable, because it doesn't need to carry a ton of fish anymore, it's bottom has been widened to improve its initial stability and increase internal volume, for the standup head and obligatory built in beer can holder/toilet tissue dispenser. Don't get too carried away with these "proven" types, as they're no longer what they once were.

    I think you need more length. The reason is, you want efficiency and a fair bit of accomodation. In order to have these things, you need to stretch the design out, other wise efficiency goes right out the window. At 24' my Cooper Jr. fits the bill, but she's not what I think you're looking for, in terms of efficiency. As 24' power cruisers go, she better than many, but still pretty typical. Now, if this same boat was narrowed a touch and stretched out to say 28' or 30', her efficiency goes up dramatically and you still get to have all the stuff you want. Think of it as a "shot gun" style of house, where the footprint of the property limits what you can do widthwise and elbow room is at a premium, so you arrange everything in a line, front to back. It's a ranch style of home, but you enter through the gable end, instead of the long wall side.

    The same is true with your boat, keep a modest beam (say 7' or so), but line up the accommodations so it's a tandem setup, rather than side by side. It's less convenient, but you'll save at the fuel dock and still get the accommodations you want.

    It sounds like you're looking for a rough and ready "picnic boat" with serious passage making abilities. This was once fairly common. Also, the "commuter" style of old river and harbor transport might be the route as well. The commuters were often narrow, efficient designs, yet comfortable and had all the accommodations you'd need, just not in a fat and wide butted boat. Have you looked at the larger "Bartenders"?

    As your first build, this would be an exception to the rule and typical learning process. Once you've settled or commissioned a design, consider building the dinghy to it first, with the same methods the mothership will employ. It's a much cheaper way to learn, trust me.
     
  10. serow
    Joined: Mar 2016
    Posts: 74
    Likes: 3, Points: 8, Legacy Rep: 40
    Location: UK

    serow Junior Member

    What are the thoughts on this range of boats?
    They look pretty nifty to me and belt along with 40hp. Would they be any good at slowish speed. In some of the vids they seem at ease before getting up to speed.
    They look easy to make and are quite light and trailer-able. According to the blurb the coastguards were quite impressed.
    https://bartenderboats.com/
     
  11. nzboy
    Joined: Apr 2011
    Posts: 154
    Likes: 4, Points: 18, Legacy Rep: 36
    Location: nz

    nzboy Senior Member

    Nice wee troller in BC for 12.5k
    5777191_20160416142029261_1_XLARGE.jpg

    5777191_20160416142029629_1_XLARGE.jpg

    5777191_20160621115554192_1_XLARGE.jpg
     
  12. Wavewacker
    Joined: Aug 2010
    Posts: 696
    Likes: 21, Points: 18, Legacy Rep: 226
    Location: Springfield, Mo.

    Wavewacker Senior Member

    Appreciate the wisdom Par, the Bartender is a very nice boat, I'd like to own that 22/24 footer and that's the cabin design I'm after. Some beautiful boats there. Serow, I'll describe my requirements that should explain why I can't go that course.

    Yesterday, I was at my office (actually it's a bar that I call my office) and mentioned I wanted to build a boat, that started a good conversation and I got a volunteer to give me some occasional assistance! He's a master carpenter by trade but hasn't ever built a boat. My tool inventory may have increased too.

    Even at that, the Bartender is beyond my (our) skill level and build time required, probably a budget buster too. I've watched the dory builds on You Tube a 20 footer was done for under $1200, I think 4 feet more would still keep the bill under $2,000, not counting the motor and trailer. I have the stove, toilet, some electrical, a trolling motor and boat nic-nacs. Not much more is need other than more hardware, adhesives, lumber, ply, glass and paint.

    Par, thanks for the heads-up on the dory, I know it's not the perfect boat. I think it would be slamming less than a garvey. Then again, low power means pretty much displacement hull speeds, no skiers LOL.

    Yes, the posts are getting long again.

    Nzboy, good point, I know buying is usually the better option. Selection is rather slim in Southwest Missouri. My motivation would be high for that boat if I were in BC. Location, location, location as they say.

    I have no idea what the draft is on a Bartender, but when I mentioned shallows I'm talking inches, less than a foot. Pretty much why I'm stuck with a flat bottom boat, dory, garvey, jon, sharpie, freighter canoe, etc....

    I'd love to have a 30-32 footer, in a way, but it's not practical for us. I had a 5,000 lbs, I/O cuddy, it was to big for me to manhandle, loading and unloading, trailering with my F-150, not to mention the real estate it took up at home.

    At 24 feet, it will fit in the garage but I'll need the door up to work on it, that also means a dolly under the strongback.

    Getting big and over 24' means a double axle trailer too. I have a single axle that I can modify for the boat. On the road the boat may serve as a camper as well.

    We can be happy with a 6' beam, that may mean only 4 on board, but for just the 2 of us and the mascot 4' might work, that's wider than a standard residential hallway. I understand narrow places limitations on a cabin. At anchor I might throw out a couple floats, amas, just some insurance to sleep with. A flotation collar might be good on a narrower boat. We do need some good initial stability however.

    In reality, this boat may never hit saltwater, 10% chance, hopefully what we end up with "could" go into good conditions in the gulf, but most of its life will be on local lakes and the rivers mentioned.

    Then this spiral I suppose is more to how to get low HP efficiency on a 20-24 foot boat. I'll toss out reducing the beam. A decked cuddy over a v berth, a higher roof that doesn't act like a sail as wind hits cabin walls, an open roof that can be enclosed with canvas would work. I don't want a 5,000 pound boat, but this can be heavily built to run up on sandbars and shore. I also have to shove it off, not sure if 10 HP would always pull me off a grounding.

    While my thinking says we may try for 80+ miles a day, there is no race, that could easily be 50 miles, the range will probably be less on a narrower boat, that's still better than a 10 mile float trip in my canoe!

    It's safety first, then efficiency, then comfort.

    Thanks again for your thoughts :)
     
  13. kerosene
    Joined: Jul 2006
    Posts: 1,019
    Likes: 57, Points: 48, Legacy Rep: 358
    Location: finland

    kerosene Senior Member

    If you think you can build a substantial boat for 2k$ you are set for failure. Look at GOOD used boats and double the price to get in ball park.

    Overly optimistic plans are if not doomed quite demoralizing at best.
     
    1 person likes this.
  14. Caroute Motor
    Joined: Jun 2016
    Posts: 54
    Likes: 1, Points: 8
    Location: CN

    Caroute Motor Junior Member

    1 person likes this.

  15. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 470, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Not for nothing, but the description for the trolling motor you've listed is a joke. It's calls this puppy the equivalent of a 9 HP outboard, yet the math says it's barely a 2 HP. A completely foolish idea for pushing a 24' cabin cruiser any faster than 2 - 3 knots on a windless, dead flat sea, not to mention you'll need a few thousand pounds of batteries to offer any kind of range.

    Standing headroom in a 24', shoal draft boat simply means you're going to have about 6' of windage, all around. Then there's the stability issue with a flat bottom boat and a standing headroom cabin on it. What you should be looking for is a sailboat hull, for efficiency and low powering requirements and its inherently better stability. Have a look at my Rocky design in the gallery here, so you can see the "5 panel" multi chine layout. It gives you a flat bottom, but offers better flow dynamics, for not a lot of extra work. You get more internal volume, can beach bolt upright and can fit in more accommodations than a V bottom or a dory.

    Stretching out this 5 panel hull shape will prove a little better than a sharpie, jon, garvey or other 3 panel design. For example if you make a 24' plumb stem and stern skiff shape, with modest side rake, say 5 - 7 degrees and a 6' beam, you'll have a 2,400 pound displacement boat, of course depending on the draft and rocker, but with conventional shapes around 7" - 8" of draft (hull bottom). Using the same dimensions, except employing the 5 panel layout, you get a 1,500 pound displacement boat if it's a double ender and about 1,800 - 1,900 if it's transom sterned. Of course, ideally the 5 panel shape would best if you could live with slightly more draft, so with 9" of draft, you'd end up with displacement similar to the 3 panel (flat bottom), but much better efficiency and flow characteristics. BTW, a 2,400 pound 24' cabin cruiser is a light baby. Light boats don't need as much to propel and don't cost as much either, because there's literally less material in the boat.

    If you'd like email me and I can draw up a 5 panel and offer simple scantlings for not a lot of money. You'd be on your own to work out the details, but with the shapes and scantlings in hand, you can cut and cuss your way through I'll bet.
     
Loading...
Similar Threads
  1. robmcg25
    Replies:
    41
    Views:
    801
  2. Schoolbus
    Replies:
    23
    Views:
    1,022
  3. upchurchmr
    Replies:
    3
    Views:
    727
  4. MurphyLaw
    Replies:
    4
    Views:
    513
  5. Wellington
    Replies:
    8
    Views:
    751
  6. Wellington
    Replies:
    12
    Views:
    946
  7. bjdbowman
    Replies:
    22
    Views:
    2,119
  8. Barron Cohen
    Replies:
    5
    Views:
    848
  9. George Gottlieb
    Replies:
    12
    Views:
    988
  10. xellz
    Replies:
    36
    Views:
    2,777
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.