planing sail boat hulls

Discussion in 'Boat Design' started by wayne nicol, May 4, 2018.

  1. wayne nicol
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    wayne nicol Senior Member

    so following on Sobells post about designers and N.A's helping neophytes with input, here is a question that i would love some input on.
    1.what would be the detriments or negatives to a sailboat with a flatter wider run aft, to assist with planing, either under sail or under power, how would this detract from, or affect the sailboats performance?

    and NO, i am not wanting to go down the Macgregor motor sailer route here.
    i have the desire and motivation to build a boat, but only because there are no existing similar boats on the market, and no existing plans on the market for this concept. Besides the macgregor, which in my opinion was very poorly executed, due to the business model being orientated around high volume production and low margin sales. So many compromises were made, both in the design and the construction of the boats.

    all input would be appreciated.
    many thanks.
     
  2. philSweet
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    philSweet Senior Member

    Flatter and wider than what?

    49er -

    [​IMG]
     
  3. rwatson
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    rwatson Senior Member

    As I understand it, having a wide stern makes higher heel angles while sailing a problem, because as the boat leans over the wide stern has to push the bow down into the water.

    To have a yacht with a planing stern, you have to be expecting a lot of the sailing to be done downwind. The problem is that straight downwind is usually the slowest direction. All high performance boats tack downwind where possible, because they get more lift. from their sails.

    I have done a fair bit of thinking over the years about the "ideal MacGregor" concept, which is what I think you are looking for. My current preference is to keep the wide planing stern for power work, but be able to use the water ballast to raise the draggy transom up out of the water while sailing.
     
  4. wayne nicol
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    wayne nicol Senior Member

    Phil, thanks for the link.
    wider and flatter as wider and flatter than the rest of the hull, as opposed to a traditional displacement sailing hull where the transom is narrower than the widest bean, and certainly no flat run aft.
    Thanks RW, good to see ya again.
    i have been looking at the C&C 30's and a bunch of different one design, high-speed sailers, they have a really flat run aft, but the stern quarters are a lot softer, and elevated , and one can see, how flat downwind- the planing hull would be effective, yet on a heel, the transom would be clear of the water.
    here's but one example- look through the pics.
    Cape 31 One Design – Mills Design http://mills-design.com/project/cape-31/
    i really like that concept, as its well proven, and i see some of that in the mac stern, except they have carried that 10* VEE right back to the transom, which creates very poor planing performance. i see no reason to have that VEE at the transom, the VEE is needed for the bow section to reduce pounding underway and other attributes.
    A flatter run aft, creating a "planing disc" would actually have created more floatation, allowing the boat to truly plane- which it doesnt do now, and also assisted with getting the transom out of the water.
    i agree totally with the use of the water ballast to engage the fore of the hull, and assist in elevating the transom.

    i really like this little boat-
    Princess Sharpie 26 | B&B Yacht Designs https://bandbyachtdesigns.com/princess26/
    and i have been talking to Tad Roberts, he's on here, and lives really close to me. i am hoping to engage him in the design of this craft, i am just wanting to learn as much as i can in the interim.

    you are correct though, still chasing the dream of the ultimate hull for my purpose. :)
     
  5. PAR
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    PAR Yacht Designer/Builder

    You seem to have some misconceptions about why a planing hull form is shaped the way it is and also seem to be mixing different forms for comparative reasons. There's two basic planing hull forms, which do have similarities, the modern sailing full plane form is essentially a triangle, progressively getting wider along the LWL. These are a result of racing and are very poor upwind, but can scream off wind. The other form is an older approuch and the planing patch is moved forward a touch, still has a wide stern, though not as wide, proportionately to modern hull forms, and it also has a more bluff bow, to help initiate the plane and hold it's bow up when going up hill.

    All boats that plane off need a flat run, with sufficient area to hold the boat up. Generally buttock angles are kept below 3 degrees and the rocker is straight or nearly so. MacGregor uses a monohedren hull form, which is more efficient at higher planing speeds and also why they carried the modest 10 degree deadrise all the way aft, unlike your assumption about it being unwise. Ideally the planing hull form is flat bottomed, with a suitable entry, but this isn't very comfortable and has speed limitations, so some deadrise is introduced to soften the ride and improve efficiency at the top end. 10 degrees is quite modest for a planing powerboat.

    The problem, other than radically trimming the boat, is the two modes of operations are in direct conflict in terms of hull form shapes necessary. The Mac 26 is essentially a powerboat hull form, with soft bilges, water ballast and a rig. As a powerboat, it's not bad, but is limited in top speed by it's soft chines and deadrise. As a sailboat, its initially stable, mostly because of the ballast and modest rig, but drags her stern, limiting her abilities. For her to plane off as a sailboat, she'd need in the area of 1,200 sq. ft. of sail, so she's screwed in this department.

    Designing an odd ball like this is all about the compromises you'll willing to accept, which is true of any design. Difficult design decisions as Ted Brewer call them, will always lead you down a path you don't like in some respects. I don't think lifting the stern will work very well, given the now immersed shapes typically used in the forward sections. If you want to go fast under power, you will have to accept some of the compromises MacGregor has or consider a multihull. Again the decisions will confound you, for example, I know of more than one sailing yacht that was considered too fast, because it was intended to getup and scoot, which is great, until you get into a crowded anchorage and have to maneuver around lots of other boats. Having to reef in 10 knots, just to manage the boat, is inconvenient to say the least. I sailed a boat like this this last weekend. It was a racer and did getup and scoot good, but needed a reef at 10 knots. A pain in the butt on a divided rig, with a short handed crew and modest 12 - 15 knot winds.

    Maybe you'd be better off developing up a solid, highly prioritized SOR and tick off the things you can achieve, reasonably and see where you stand.
     
  6. wayne nicol
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    wayne nicol Senior Member

    Thanks Par, some solid info there.
    a boat like the macgregors are certainly a compromise, and some pretty big compromises in some areas.
    just really trying to get a better handle on what i need or want so that i can communicate my brief more comprehensively to the N.A.
    i realize the Macs do neither well, i have a mac M, also have a dedicated sailboat, and have had some smaller powerboats in the past.
    just right now for our situation, the powersailer concept works incredibly well.
    The Mac has served us well, despite its many shortcomings, and i am not referring to the design shortcomings, but rather the poor hardware, cheap sails, cheaply appointed trailer and boat. but the concept is awesome.

    However, for extended stays on board, we could really do with something a bit bigger, but i also would like something a lot easier to rig and de rig, and easy to use in powerboat mode. the mac is a pain, dont let anyone tell you they can rig in 15 minutes. so if one wants to get out for a few hours of fishing in an afternoon, its a major exercise.

    anyway, a question for you PAR, looking at the mac hull, not anything else, do you see the possibility to improve on it in anyway, if you were starting from scratch- academically speaking, still giving it the ability to motor and sail ok!
    does not need to be spectacular in either category, but do you see room for improvement.
    many thanks.
     
  7. rwatson
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    rwatson Senior Member

    This is as far as I have gotten so far. My priorities were
    1) Self build - hard chine in ply
    2) Self tacking
    3) A true 20 knots under 70 hp OB, 28ft LOA
    4) Stern and Under cover nav station
    5) I went twin daggerboards to conserve interior room, but this is optional
    6) Water ballast and all the other features of the Mac 26


    RPG01.png RPG02.png
     
  8. wayne nicol
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    wayne nicol Senior Member

    PAR, I read the thread by Doug Meyer, who was converting a trailer sailer to a power boat.I got a lot of insight to what you were saying about the different approaches to planing

    Nice RW,it seems to be coming along pretty nicely, how did you model tests work out?
    How does that hard chine affect sailing performance?

    Like PAR suggested, I need to Mae a list, I have long had a list of priorities and needs. And in no particular order
    -Increased performance-if I can get it
    - more traditional styling, I positively can not stand the euro styling of the Mac.
    -glass over foam construction
    - free standing cat ketch rig( balanced lugs)
    - pilot house with inside helm for power boating ( we live in a coastal rain forest) and trunk cabin. Standing room in the pilot house area, for shower, helm, and galley, the trunk cabin would have the dinette, seating area, and stove, and access to the V berth
    -removeable tiller for sailing mode
    -10' beam ( we can get an annual permit for 10' wide)
    - so maybe a length overall of 33' or so
    - twin motors for redundancy, even though I will only use the boat in reasonable conditions, we are extremely remote.
    - a proper 20 kn under power as well
    - a combination of permanent internal ballast and water ballast.
    -either bilge boards or lee boards. As they can be angled better to have a greater effect, and be assymetrically shaped.
    I really like the idea of leeboards controlled by a car on a track, so when sailing on main only, for example when fishing or any other reason, I can trim the helm for balance with the positioning of the boards.
    I also like the idea of no trunks to jamb up with mud and debris, we don't have nice sandy beaches, it's all mud banks.
    I like being able to pull the boards up, stow them on the trunk cabin, masts, spars and booms in the gallows and be in total power boat mode.
    -on open, uncluttered cockpit. We do a lot of food fishing here. Part of our total diet, not recreational fishing.
    - proper head and shower on board, with more space than the Mac. Large stern berth, and V berth . Decent galley, fridge/ freezer, and a small wood or diesel/ kerosene stove to deal with the humidity and condensation. We like to boat all year round. Hence, good reason for the foam core as well.
    - this boat needs to trailer easily, living on an island archipelago , we need the versatility to be able to use a variety of launch sites, some 60 miles from each other,but we need the speed, because if I launch from my town, it's a 40 mile run to the fishing grounds, down the inlet. weather can also pick up in a hurry out here in the PNW. So we need to be able to run and hide, but we also do a lot of cruising at 5-7 kn.
    -I like to sail when trolling, I also like to sail recreationally, and we , as a family like to motor to a gunkhole, then spend a few days sailing and living aboard, then power back to the dock, then trailer home.


    I think that covers most of it, may be a few things left out.
    I have thought about a power boat, and a sail boat, but just can't get them to work effectively for my situation.
    We love to sail, but are not racers, we like to puddle around with the family, with over 500 islands in the archipelago , we have lots of squalls, wind shadows and wind tunnels, hence the choice of rig, that has a lower COE, and is easy to de power. We can find ourselves switching from power to sail a dozen times in a day, if not more.

    Many thanks
     
  9. wayne nicol
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    wayne nicol Senior Member

    http://www.in-time-yachts.fi/images/pdf/sailjet-sloop-rigged.pdf

    they seem to have pulled off the flatter planing area at the transom, with the chines.
    how would those harder chines effect the sailing performance.
    they do seem to have a bunch of HP in her though. but its a LOT more boat.
    although in the videos, it does not squat any worse than the mac at powering speeds.

    http://www.macgregor26.com/powering_and_waterskiing/powering_dale_large.jpg
    http://www.in-time-yachts.fi/images/pdf/sailjet-40-brochure.pdf
     
  10. wayne nicol
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    wayne nicol Senior Member

    Ray, i am picturing the underwater profile of your boat being very similar to the sailjet40 ?
     
  11. PAR
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    PAR Yacht Designer/Builder

    Having a well behaving sailboat that also happens to power well just isn't going to happen. The hull forms are too dissimilar for a reasonable set of compromises to be attempted. You can have a good sailboat that's a moderately good powerboat, though likely not able to handle a big chop well or you can have a good powerboat that sails poorly, but at least does.

    Styling and aestedics are purely "add on's", so this is discounted. The pilothouse and rig choice will detract considerably from windward ability, so you're not going to get an uphill monster. Twin engines may sound nice, but the reliability of engines today makes this unnecessary. Modern aircraft have engines that are hung under a wing and left there for 20 - 30 years. Yes, they're maintained, serviced, etc., but the engine hangs there until the air-frame hits its hours limit. The same is true of most modern engines. You drop it in the bilge and it lives there, until the boat is dragged to the land fill some years later. Redundancy is great, but for things as heavy as engines, maybe some other accommodation would be wise. At 20 knots, you're traveling at 2.7 S/l ratio, well into semi plane mode. In fact at this speed you're on plane, though the bow may not have settled fully yet. This means the hull is a powerboat, further detracting from sailing abilities. You're looking for a motor sailor, not a sailboat, with emphasis on motoring, not sailing. Assuming a 30' LWL, you displacement speed will be 7.4 knots at S/L 1.35. Assuming you'll back the throttle a bit while cruising, this is 6 knots, which is right were you'd like to me. You can get greedy and ask for more than a typical sailboat can do, or accept the compromises you've established and live with a little better then cruising speed with a bigger engine.
     
  12. wayne nicol
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    wayne nicol Senior Member

    Thanks for your insight PAR, as to redundancy we have all sorts of other issues up here other than just motor reliability.
    we have a lot of deadheads in the water- i have hit deadheads at least three or four times in the last half dozen years, i have cooked two two impellors with kelp wrapped around the water intakes( true , on an older motor- that did not have a temp warning system) did it once on my new evinrude, and managed to forestall a problem.
    i have seen a lot of boats towed in here over the years- always engine/prop problems of one sort or the other.

    i hear you on the motors reliability- and i agree. ( however i must add- that those aeroplane engines... they all have dual everything on them, fuel pumps, alternators fuel systems, electrical systems, dual plugs per pot etc etc)
    this is all seismic generated coastline here- so channels are deep and the bricks are close- you can be in a channel thats 300' deep straight against the rocks, currents commonly rip at 5 to 6kn here, its not a place to be sitting with a dead motor, even if its just a fuel issue, often cant drop the hook to keep you off the beach. pretty much every boat that hugs the coastline here-( protected waters), has a secondary motor of some sort.
    so just going by local knowledge, i think it would be prudent for me to consider some redundancy, even if at a cost.

    For times we need to buck the tide- a 6 kn boat is going nowhere, i mean we get creative with back eddies etc, but thats where a 20kn boat will get you home, albeit a bit slower. Just the way it works, i cant wait 6 hours for the tide to change for me to come 30 miles back up the channel.
    the pilot house and trunk cabin would actually be a reduction in windage compared to what i currently use, but yes it does come with its share of compromise, if i want a stand up shower and galley and inside helm, i understand that it will not perform, like a low slung, dedicated sailboat.

    i know the rig will be a compromise, but this seems to be the only way to resolve some of my criteria, if there are any other suggestions around this, i am more than willing to consider them.
    but i need masts that are no longer than bow to just aft of the pilothouse bulkhead. i need to keep the cockpit uncluttered when powering.
    i need unstayed masts.
    the luggers or sprits ( maybe too big of a boat to be a good choice for traditional sprit sails) seem to get the most canvas aloft for the shortest masts, a split rig would benefit that even more, also reducing the heeling somewhat.
    at a price? for sure!

    The bottom line to all of this, is i am more than happy with the Macgregors "sailing" performance- i know its no where near the performance of a true blue sailer- but i am happy with it, the mac concept really works well for us, what i need to know, is can the macgregor hull be improved upon, to improve its power boat capabilities without compromising its " sailing" capabilities.
    as we want a bigger boat, with a different rig.

    sincerely, many thanks for your input, i like adding some reality and balance to my thoughts.
    better to hash this out here, so that when i go to the NA, i am better edumacated!!
     
    Last edited: May 5, 2018
  13. sharpii2
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    sharpii2 Senior Member

    I recently wrote an article describing the the design compromises mentioned above, for this type of boat, for Small Craft Advisor. They published it and actually paid me :).

    The boat concept I described was much smaller, only 20 ft. But it had a very low rig, to get its sailing power as close to the waterline as possible. This was done also because the boat was not likely to perform well to weather anyway, and the desire was to have a rig which could be set up and taken down in a minimal amount of time, and while the boat was in the water.

    The boat you describe is likely to displace 4 to 5 tons, at a 33 ft length and a 10ft beam. A full planing 20 kts seems to be a bit much here, as it will require a bigger engine and bigger tanks, which will require even more buoyancy aft to support them. This will likely mean a wider and deeper transom.

    Would you settle for 15 kts?

    15 kts seems to be fast enough to get you out of Dodge, against the currents you describe.

    This speed may be possible with 15 to 20 hp per ton.

    The 20kt speed may well require 40 to 50 hp per ton.
     
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  14. HJS
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    HJS Member

    For several years I have sketched a motorsailer. In my humble opinion, you can create a planing motorsailer with good performance under sail and power. The reason for this view is my positive experience with my multichine boats and powerboats with adjustable aftship interceptors.

    http://sassdesign.net/Interceptors in theory and practice.pdf

    First, I calculate a sailboat hull according to the rules of art as usually. Then I calculate a planing bottom of a powerboat with an adjustable aftship interceptor. It is important that the total center of gravity must be the same in all calculations. No guesses allowed. Here are no compromises, just optimization.

    Then I bring these two concepts into one hull with good qualities in all situations. To increase the righting force during sailing, I have also added an adjustable interceptor at waterline amidships.

    This shown sketch is a first draft that shows the principle. At the next stage, it will of course be adapted to the customer's wishes and the builder's possibilities.


    Motorsailer w aftship interceptor b jpg.jpg
     
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  15. rwatson
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    rwatson Senior Member

    Excellent. I remember discussing this many years ago.

    Have you had a chance to build any prototypes over that time ?
     
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