Shanty Boat Hull Modification Questions

Discussion in 'Boat Design' started by Bing, Nov 12, 2022.

  1. Bing
    Joined: Jun 2006
    Posts: 39
    Likes: 4, Points: 8, Legacy Rep: 16
    Location: New Hampshire, USA

    Bing Junior Member

    I’m hoping to get some help from the forum regarding my 1969 Aquacamper Adventurer. We purchased this boat in 2016 from a family in Illinois, who had kept it in a barn for 47 years, unused apparently but for the 3 hours showing on the 90hp Mercury engine gauge. The plastic wrap was still on the cushions. After a very eventful trailer tow east, we’ve kept the boat for five seasons in Whitehall, NY, at the top of the Champlain Canal and the southernmost tip of Lake Champlain. Terrapyn (the Rohirrim spelling of the testudine) has proven to be a lot of fun for my wife and I for short cruises on the NY canal system and the lower, narrow portions of Champlain.

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  2. Bing
    Joined: Jun 2006
    Posts: 39
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    Location: New Hampshire, USA

    Bing Junior Member

    She’s 23 feet long, 7 feet 9 inches wide, and displaces about 4,500 lbs. All-in trailering weight is about 5,700 pounds, and due to the front vertical surface of the cabin, tows like it weighs twice that amount. Construction is plywood sheathed in fiberglass and polyester resin. There are no stringers or frames. Instead, the long defunct Illinois manufacturer (about which I’ve found almost no information) used two layers of 5/8’s ply on the bottom, including the sweep up at the bow, and ¾ plywood hull sides, which makes for a surprisingly stiff hull. As far as I know, I may have the only Aquacamper still afloat (I know of one other, but it’s used as a static studio in a pasture). The way I installed new cabin furniture increased this stiffness somewhat, as the original interior partitions provided nothing in terms of structural support. I sold the original 90hp Mercury (I can’t imagine that much power on the stern, especially as the transom was so weakly constructed – now reinforced). The 30hp Honda four-stroke (what I could afford at the time) pushes her along at a leisurely 5.2 knots at 3000 rpm, using a little less than a gallon per hour. Yes, she is bit underpowered, so I’m looking to upgrade to a 40 horse, perhaps a 50 horse hi-thrust. I think the fuel economy would improve a little, and the extra umph would be great in tight maneuvering situations. I’m not expecting an increase in speed, although I wonder what the displacement hull speed actually is (waterline length is 21 feet 3 inches, drawing 7 inches of water exclusive of the 5 ½ inch skeg and motor lower unit).


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  3. Bing
    Joined: Jun 2006
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    Location: New Hampshire, USA

    Bing Junior Member

    I remodeled the interior a couple of summers ago to make the galley more efficient, increase the size of the head compartment (we use a C-Head composter), and to make the seats much more comfortable. She’s set up for cruising for two in two single bunks, which can also be re-arranged into a double bed. For day trips we can seat four at two settee tables. The Dickinson wood stove makes early spring and fall trips quite cozy. She’s awfully comfortable and very easy for an aging couple to handle. But Terrapyn does have issues.


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  4. Bing
    Joined: Jun 2006
    Posts: 39
    Likes: 4, Points: 8, Legacy Rep: 16
    Location: New Hampshire, USA

    Bing Junior Member

    Obviously, she’s a calm water boat. The scow hull isn’t suitable for Lake Champlain proper, as her bow slaps like a beaver tail in the smallest of waves, and clearly her low freeboard isn’t meant for open water cruising. But that’s OK, since we bought her for cruising the 525 miles of the NY State Canal System (Erie, Champlain, Cayuga-Seneca, and Oswego Canals). The only dangerous waters we occasionally experience are those created by deep draft cruisers passing by much too fast, which is why it’s a standing order to keep the lower half of the front cabin door closed at all times while underway. When we fall into a boat wake pit we can get quite a charge of water over the bow, but fortunately that sheds off immediately the way the bow coaming is designed. Plunging into a boat wake isn’t a problem that I’m looking to correct as there’s nothing one can do with a flat bottom boat but slow down and turn to take the wake at an angle to lessen the drop and roll. I’ve gotten good at that, and have learned to hail bigger boats ahead of time if they don’t look to be slowing down.

    Here’s the first problem. Terrapyn does not track well and thus requires constant helm adjustments to steer a straight course. My wife refuses to steer because of this, and frankly, it’s not a lot of fun for me, although we try to limit cruising time to no more than 2 to 4 hours per day. Terrapyn’s skeg keel seems to be inadequate, further evidenced by how easily the wind can play havoc with one’s approach to a dock. So my first question is what modifications to the hull could I make that would improve her tracking? I’ve thought about adding a box keel or maybe leeboards, but I don’t have enough experience to know what might be the most cost-effective solution. A friend suggested putting those bolt-on wings on the motor skeg, but I’m not sure that’s what those are designed for.

    A related problem, which I understand is a common issue with scow hulls, is the wave slap under the bow when at anchor. It’s relentless and makes sleep impossible. I’ve learned to rig the anchor rode, once the anchor is set, with a trip line off the stern to pivot the boat so she sits with her stern quarter to the wind thus spoiling the wave slap. When I’m ready to get underway I release the stern line and she swings her bow back into the wind. I’d sure like to not have to do this though. And bow on to the wind she dances around the anchor rode like a leashed, nervous possum, which can be alarming when you wake up at night to check your anchored position and find yourself momentarily disoriented because of all the swinging. In a crowded anchorage, Terrapyn would be a menace. I’m sure this pivoting is due to the inadequate skeg.

    The third issue I’d appreciate help with isn’t regarding a problem, but an improvement I’d like to make. I’d like to have a back porch that can be enclosed with screened canvas for evening relaxation on deck in our bug filled summers and to allow for two sleeping cots. I can think of two options: extend the stern about 3 feet which would give me a deck about 6 foot 6 inches long, or, use the boat like a tug and push or tow a small pontoon boat (say a 12 footer), which could have a collapsible bimini with screened sides. Lots of pros and cons for each option.

    So those are my questions, which I hope will be a fun exercise for the forum. My son and I are fully capable of constructing the modifications that may be suggested, which I’d like to complete next summer. My wife and I want to spend the 2024 season cruising the entire canal system. Thank you.

    Tim Jennings
    Enfield, NH
     
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  5. mc_rash
    Joined: Aug 2020
    Posts: 91
    Likes: 28, Points: 18
    Location: Netherlands

    mc_rash Junior Member

    Nice job done with the interior, I like it. I searched on Google for your boat and found your entry at a houseboat design competition.

    If you are planning to extend the the hull for your relaxation deck you could also extend the skeg aftwards (not only in length but the also in height). See the green shaded area in the attachment. This would give you two advantages:
    - more deckspace for example for your relaxtion area
    -better steering handling/ keeping straight course
     

    Attached Files:

  6. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Pretty pretty pretty little craft

    Is she stored on a trailer? Changes to the keel might require changes to trailer.

    I would increase depth of keel. Especially aft

    Do you anchor from the bow's center? Have you tried anchoring from just aft the the coaming??

    A riding sail on the aft would calm the possum.

    She appears to be down at the stern. An outboard bracket and tent structure would bring her stern down even more. Extending the hull would level her sheer.
     
  7. mc_rash
    Joined: Aug 2020
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    Location: Netherlands

    mc_rash Junior Member

    I found an article you might find interesting (or not). It is a CFD study about wave drift force and directional stability, comparing a hull without and with added skeg(s) (they added two). I'm posting it because this vessel looks pretty similar to yours but, assuming your boat is extended by 3 ft, scaled up by a factor of ~11.55. If the 3 ft aft are added to your boat also the relative dimensions are pretty similar to that of the barge in the article.
    Since it is a technical article I'm not sure if it has any value for you but still you might find it interesting to read.
     

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  8. Bing
    Joined: Jun 2006
    Posts: 39
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    Location: New Hampshire, USA

    Bing Junior Member

    Thank you for these replies.

    Is she stored on a trailer? Changes to the keel might require changes to trailer. I would increase depth of keel. Especially aft. Yes, she is stored on a trailer, which I modified to permit the addition of a larger keel, so this would be no problem.

    Do you anchor from the bow's center? Have you tried anchoring from just aft the coaming?? Yes, the bullnose is dead center on the bow. I don't know why I didn't think of using the forward spring cleat instead of the stern, as I could easily do so. Maybe that would put just enough angle on the bow to correct the problem. I hadn't mentioned that I was planning to install some sort of anchor pulpit to keep the retrieved anchor outboard of the bow because the bottoms in our cruising areas are generally very thick, sticky mud. It would not be a problem to shift the mooring cleat angle to lead the rode off center.

    A riding sail on the aft would calm the possum. Yes, I could see that working. I wonder that what I have in mind for an aft canopy might serve a similar purpose, as it would provide a slightly taller sail area back aft. But then if a deeper aft keel improved tracking, I wonder if it wouldn't also lessen the anchoring swing to compare with a normal shaped bottom boat.

    She appears to be down at the stern. An outboard bracket and tent structure would bring her stern down even more. Extending the hull would level her sheer. Actually, she rides right on her lines with 7 inches of draft both at the bow and stern. I think the photo angle of the boat next to the dock float misleads the eye. I shifted weights around (batteries, water storage, and other heavy interior components) to keep her level. The hull has a straight sheer.
     
  9. Bing
    Joined: Jun 2006
    Posts: 39
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    Location: New Hampshire, USA

    Bing Junior Member

    Here's a picture of the bow when it was up on stands. In my earlier post I had forgotten about the two smaller skegs outboard of the center skeg.

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    Here's my interpretation of your suggestions about increasing the length and depth of the after part of the skeg when I lengthen the hull.

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    Is this about right? I'm showing the extension about 12 inches deep. I suppose I should shape the aftermost edge of the skeg to a point to permit smoother water flow to the outboard propeller.

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  10. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Ah, the cleaver deception of photos.

    I suspect the bow skegs are intended for beaching protection rather than tracking aids.

    The new porch tenting will help. But not as much as a true riding sail would.

    I would extend the deeper keel to mid ship.
     
  11. Bing
    Joined: Jun 2006
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    Location: New Hampshire, USA

    Bing Junior Member

    An updated sketch showing the new skeg extension running to mid-ships. 12 inches deep seems a bit much to me, so this is shown at 8 inches. I think I can easily fabricate this by screw and resin gluing
    two cheek pieces of 3/4 ply on each side of the existing skeg then pinching them together at the aft end to create a bit of a foil shape. Fill the void with wood and rigid foam as makes sense. Fair the leading
    edges of the cheeks forward, then glass and resin the whole thing to the hull.

    Is 8 inches too shallow?

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  12. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Looks great to me.
    But I'm not a NA nor am I footing the bill.

    Your approach seams reasonable. And it would be easily alterable if further refinements are warranted.

    8in depends on how shallow your canel is, and trailer clearance. The larger the skeg is the greater its effectiveness. Too long and you might be able to only go straight.
     
  13. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    She is a lovely wee houseboat for sure.

    Re the sketch posted above by @mc_rash I would prefer something like this, with a bit of rocker on the hull in way of the extension, rather than extending aft with the chine and keel lines parallel.
    Could you maybe have a bit of rake on the keel, with the depth of the keel aft (not allowing for any rocker) being say 12" (4" deeper than the keel depth at the forward end)?
     
  14. Bing
    Joined: Jun 2006
    Posts: 39
    Likes: 4, Points: 8, Legacy Rep: 16
    Location: New Hampshire, USA

    Bing Junior Member

    As I understand things, if the bottom curved up to just below the waterline at the stern, I'd have less drag at displacement speeds. But that makes construction of the extension much more complicated. The existing bottom ply is 1 1/4 inches thick, and where I need to sever the old stern from the hull leaves about 36 inches of new bottom to add to effect my desired 6 ft 6 in aft deck. While yes, I could laminate 5 layers 1/4 ply to a curve to form the stern rocker, that curve would need rise up about 4 to 5 inches over the 36 inch length -- not very subtle. Now if you guys told me that I'd pick up a couple of knots of speed by going to all this trouble, I might re-think my approach. But Terrapyn is essentially a barge. Will the performance be all that much better if I do this?
     

  15. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    You could perhaps have the the bottom coming up as a straight line, rather than a curve - that would certainly be easier to build, re how it is 1.25" thick.
    And you won't see it when she is afloat.
    You will definitely have less drag at displacement speed, but you will also lose some buoyancy at the back, which is probably a good thing, as you ideally want her to trim slightly down by the stern.
    If you do not give her some rocker in the side elevation, then you will have a lot more turbulence behind that transom, which equates to more drag / less speed.
    Re if you would pick up a couple of knots of boat speed - I think that would depend on how much power you decide to install.
    Fit a big enough engine and you will definitely go a bit faster.....
     
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