rough draft of 28ft trailer/sailer/power cruiser with water ballast

Anyone seen or built a rotating hull frame ? (for a 28ft X 8 ft)

Some months ago I dropped a line in the occupations forum asking for a designer to help with a boat concept that I would like to build and own.
I got some great responses, and was able to organise a designer to help.

I have attached a PDF of the first rough draft he sent through. Something I didn't know is that it is possible to get Adobe Acrobat to behave like a 3 dimensional viewer, and this attached PDF will do that, if you have the latest version of the Adobe Viewer installed. It makes a great way to spin and view boat designs.

I am also very pleased with the outcome of the design. The brief was to design what is essentially a competitor to the MacGregor design, with a few 'extras' to improve the experience.
As an ex Mac owner, I liked the water ballast concept, the trailerability, the relative roominess and the ability for fast power as well as sail. The current design with the rotating mast was something I would have liked back then, and I will incorporate in this boat as well.

The main extra features I requested (besides being a bit longer) are:-
1) A cabin suitable for sheltered navigation while under power.
2) Self tacking jib.
3) Water ballast tanks that are able to hold flexible fresh water tanks for extended cruising. (As the fresh water ballast gets used in drinking, washing etc, the ballast burden is taken up by seawater)
4) Twin daggerboards for increased interior space and slightly reduced depth. (the ones in this drawing are a tad exaggerated, I know)
5) Hull design to cater for up to 100 hp outboards.
6) Proper head, shower and holding tanks.

Based on my experience with the Mac, I am also going to add some extra features to overcome operational glitches, like -

A hinged 'bowsprit' to double as an anchor holder as well as a highfield lever for the forestay. It was such a hassle to get decent tension on the forestay with a self furling jib on the Mac. This 'bowsprit' will be hinged at the back so tension can be placed on the attached forestay. The bowsprit will be a U channel to accomodate the shaft of an anchor, to make deploying and retrieving acnchors easier. The bowsprit, being hinged, will be able to be folded out of the way while trailering.

I am going to incorporate a small mast tabernacle, with a point to attach the boom to when lowering the mast. In the older version of the Mac, there was never any easy place to stow the boom and mainsail when the mast was being lowered. The tabernacle will also be designed to be a bit more helpfull in mast lowering too.

I would like to fit a longer range interior fuel tank. Manhandling two full plastic tanks was a real pain in the back, and they didnt provide a decent range.

Rather than a bench seat, I plan to have a 'saddle' seat like a jet ski. It was tiresome to spend an hour or so heeled over while sailng, and having to have a bent back with your bum sliding to leeward. With the 'saddle' design, there will be something to brace you feet against when standing as well, rather than just a slippery sloping deck.

I have some refining of the design to go yet. This version shows the outboard embedded in the stern, which is probably a drawing anomaly. I requested a slightly fuller bow for increased interior accomodation. I dont like the bench across the cabin entrance either.

Originally, I expected the daggerboards to be sloping outwards, but I can see virtue in inward sloping. It takes less room up inside the boat, and when overpowered, should be less inclined to 'trip over' the leeward board.

I am still undecided on hull construction materials. I have thought about plywood, foam and fibreglass, end grain balsa, strip planking etc. I won't be doing any moulds until sea trials prove the concept.

I will be building an oversize metal trailer with levelling legs to build the hull on, so that I can move it around between tradesmen. I would like to have some kind of support at both ends of the trailer to be able to rotate the hull during building

I am hoping the design may end up being commercially available, but I will be happy if it just lives up to my needs at a minimum.

I hope it doesnt take years like my last project.

 

Any one have a Design for Rotating Formwork

I am trying to settle on a design for a framework to build my 28footer on, so that I can rotate the hull on demand for laying up fibreglass, painting etc.

Has anyone seen or built something like this before ?

Opps - wrong place - moving this question to BoatBuilding.

 

Getting Nearer to the Final Lines

Slow but steady progress.

Finally got the layout, profile, and stability calcs done.

The NA says it should work. But what would he know

He certainly can design better than me.

Should be getting the final lines in the next week or so.

 

Excellent Design Job

I got a final 3d PDF based on the 'final' hull lines for review today. This 3d PDF is a fantastic way to view concepts - makes review of designs so easy with the free Adobe reader.

I am very impressed by the way that the final version has turned out. It really pays to get a professional designer to do the hard work.

The next stage is to build a metre long model from the plans to do some tank testing, and spot any potential 'gotchas'

 

Whats with the daggerboards pointing inwards? They will be less efficient as the boat heels. Are you planning on using them as hydrofoils or something?

 

My thoughts on similar boat design.

Squidly-Diddly
Junior Member Join Date: Sep 2007
Rep: 10 Posts: 60
Location: SF bay
MacGregor should have twin fresh water ballast bags inside
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the water ballast tanks, installed through round hatches cut into the tanks. These could be used to transfer a lot of weight quickly and safely from side to side so that using water as ballast (vs lead carried deep) could become an asset not a 'compromise'.

Also nice to have 60 gallons or so of fresh water.

The bags could also be rigged to "blow" for as low pressure compressed air would be one way to pump the water from side to side.

Also, the fixed lead keel needs to be replaced with 6-8 marine batteries. If the batts go dead they will still function at ballast. It would also be nice to be able to toss the weight overboard in emergency, or loan out a batt or two.

Both these mods could be done without effecting the existing dynamics of the boat, just some interior fiberglass cutting and remodeling that wouldn't even need to be re-finished cosmetically.

PS due to tightening regs, it might be useful to install holding tank bags as well.





Squidly-Diddly
Junior Member Join Date: Sep 2007
Rep: 10 Posts: 60
Location: SF bay
My two designs-stretched Macgregor and "Cat in the Box"
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The stretched Macgregor will be much like a the M26...but to the max trailering length of under 40'.

Except that the 'perment ballast' will be a big bank of easily accessible 12 volt batteries and the water ballast will be two separtate tanks (actually more like 4 to have bow/stern trimming as well as more options for fuel, fresh, blackwater, diesel AND gas, etc.

The Macgregor 26M is a nice design, but with just a minor mod to the interior floor mold Mr. Macgregor could have 6-8 batteries and 100 gallons of fresh water. The batteries would be a nice alternative to firing up the 50 horse outboard; they make 2 hp electrics for pushing pontoon boats and you could fit two on an 26M outside the twin rudders.

I'm almost tempted to do some serious mods to a 26M. I'd have the shower be outside in the cockpit with a self coiling hose and electical 'on demand' pump and water heater. The 'fresh water' ballast wouldn't need to be drinking water, just for lots of hosing off before entering the cabin. I'd rather take a shower outside rather than try to keep clean using some problematic 'in boat' shower.

An outside in the cockpit shower wouldn't need a grey water tank as you would be just rinsing 'the great outdoors' of people and things before entering the cabin.

Water ballast in a great idea for a trailerable boat, plus water wont pull you to the bottom like lead will. But to be a decent sailor I think you would want to be able to transfer the bulk of it from side to side.

The Cat in the Box would be a 40' cat with 40' x 4' hulls connected by poles decked with either a tramp or some sort of solid removeable decking.

I'm thinking of a aft wishbone mast cutter rig with a third windsurfer type sail aft. I'd use spare sails to construct a 3 sided tent on deck.

In either boat I'd consider using the trailer frame as a aft wish bone mast. I'd even have provision for detaching the wheels and tires and mounting them on the flat on the deck as fenders so nothing would need to be left on shore.

I think it would be possible to carry the tow vehicle itself on the deck of a Cat in the Box, including ramps for on-off loading. The 'killer app' would be to tow the boat to the beach, lauch the boat, expand the scissors (poles) to separtate the hulls, use the trailer as the mast, drive the tow vehicle up ramp (or pull up with winch) and sail away. Reverse at next land fall.

 

This boat features transferable water ballasts.

http://valerieperez.com/_wsn/page3.html

It was for sale on Craigslist a couple years ago.

Said the ballast could also be quickly expelled in an emergency for extra flotation. Transferable ballast is supposed to really 'make the numbers work'.

The superstructure/canopy was fixed. 40' long and not trailerable. I asked her about a weighted retractable daggerboard/bulb(maybe even holding some lead-acid batteries) and she said all non-fixed keels seemed dangerous off-shore.

Personally, I think advances and cost reductions in machining and mechanical design can make the moving parts safe and affordable.

 

I have come to see that the movable ballast that counts is the ballast that you can move on or off the vessel. You can always move gear/ passengers from side to side and forward and aft or to the center line or skin side to achieve speed or sea kindliness. For an ocean going vessel that can be fitted out with a water maker, the MacGregor style water ballast is ideal. Here you would convert the sea water in the ballast tanks to drinking water and move that water off the boat (and a portion into jugs or bags) in the doldrums if that made sense.

I am not certain about the M but the Mac26x water ballast tanks are baffled. The X was designed to be sailed with or without the water ballast and is more versitile that way. The baffled tanks mean that we take on and jettison water ballast while underway (under sail or power).

I think you will agree that you want the tanks full in stormy weather. Hence this notion of positive flotation. I appreciate that you could empty the ballast tanks for flotation purposes but then stability is everything. It is well recognized now that water ballast eases a bad sea. Closing hatches does the same thing as this notion of using the water ballast tanks full of air for flotation.

When you start chatting in shore racing then the machinery becomes an issue. Retracting and canting foils takes time and if doing so slows down a tack then your race courses are going to be limited (or expanded depending on your perspective). Obviously anything the eliminates a tack is good for the mechanicals. We are seeing that is especially true with the Open 70s this week. The course has been optimized for the spectators, not the boats, and hence many tacks are necessary for each rounding. The canting keels slow down each tack when deployed as they are on a streight line corse. Of course the canting keels can be locked like a regular keel and I expect the Open 70 choreography involves just such a maneuver.

In the absence of a design rule, it is important to note that there is no reason to think a bulb on the end of a foil advantageous for a sail boat. The one exception would be on a sailboat where the speed through the water could be carefully regulated so that the shape of the bulb were optimal. Because sailboat speed through the water is usually variable - it takes a lot of dismissal of reason to advocate bulbs. This is especially true when the surface area of the foil and turbulance created by the bulb is considered. It takes a power boat designer to see this perhaps.

Frank L. Mighetto
Murrelet
1999 Mac26x

 

Yes, the angles of the boards will alter their effectiveness on different heeling angles.
basicaly, the angle is purely to keep the interior as roomy as possible. I did have them coming though the cabin roof, but that had to be changed as the board casings would have blocked port and starboard navigation views when being steered from inside.

In actual fact, the angles wont be any less efficient than straight down or splayed. No matter which way you angle them, one will be come more efficient, on less efficient, or if the are both straight down, they both become less efficient.

When they are splayed inwards, one benefit is that the windward fin becomes the driving fin, while the leeward fin provides less resistance. This means the righting moment is greater on the windward side, while the leeward side doesnt "dig in" with the potential of "tripping over' in a gusts.

I have seen a few of the ocean racers with their daggerboards (complimenting canting keels) with the inward sloping boards - probably for the same reasons.

 

Re water ballast - I have toyed with a few exotic ideas to take advantage of the method.
At a very basic level, I will just be ecstatic if I can make fresh water be ballast, and as it gets used, replace it with salt. (my idea in August 2007 - Sqiddly wrote it in September 07 - does that mean I win )
Having that much fresh water in a small boat like this is very rare.

I will build the inlet, outlet system with a view to say dumping the leeward ballast quickly, independant of the windward side. I sort of have this vision of trying to get over the top of another boat on a beat, and by suddenly losing the weight on the lee side, clawing closer to the mark.

On the next tack, just before going about, I could drain the higher windward side to the lee side, so by the time the bow has come around, I have the ballast on the windward side again. Sounds like a good theory - but there is a lot of testing and finessing to do before I get that organised.

As far as permanent ballst, I am going to try and acomplish that with very solid hull bottom construction. eg using very tough heavy wood/and or epoxy on the bottom of the hull where collision, groundings, trailer pressures will occur. Seems silly to have lumps of lead yet still have a "soft bum".

The battery ideas are very good. I think getting them as low and as many as possible is a great concept.

Someone suggested I could have removable lead weights in the daggerboards in serious sailing events. I have that in mind as an option. Certainly, having a suite of boards for different conditions and experimenting is on the cards.

I am lying awake nights thinking of easy ways to get variable attack angles on the foils when I should just be concentrating on finishing the bloody thing

 

Another reason for massive battery bank is convient

and cheap electrical appliances. Everything from On Demand Hot Water, to microwave ovens, to hair dryers, to coffee makers.

Instead of shelling out big money for special nautical stuff you can just grab some of the excess counter clutter you already have.

While a Marine Environment may take a toll on that $7 Chinese electric stove element, I'd worry less about it than a high priced alcohol or whatever stove inside the cabin.

I'd like to see someone do a "Hybrid" motorsailer with enough battery to comfortably get in and out of most harbors without starting the engine.

If the engine/generator was 'divorced' from the prop the design could be optimized....somehow. If nothing else I imagine the cost savings of just dropping in a generator anywhere that is convenient VS installing a marine engine that connects to the prop might cover the cost of the big electric motor for the prop.

Reading WW2 Submarine novels, I always struck me as niffy that they could surface cruise on silent electric power quiet well.

 

There is a lot of discussion on deisel/electric setups around the forum - very efficient but very expensive to setup.

When 4 stroke outboards are well tuned, they start easy, run without much noise - and they are outside.

I used to have a small Honda standalone generator - it ran quietly, started every time and hardly even used any oil. On a long trip it could be a real usefull thing for making life aboard comfortable.

The cheap camping gear concept is very valid - you can pay a lot for "marine" quality gear. Stuff like navigation aids you can take off the boat is good, from a security point of view.

All going to be a major research effort - I bet more and more stuff will be available for christmas

 

Continuing discussion - Hull Design, Version 2

From http://www.boatdesign.net/forums/al...-personal-link-thread-40721-3.html#post643524


Yes, very valid points. The cockpit roof has been a source of continual discussion between the designer and I.

The 'consensus' here is trying to get a good aerodynamic solution, (hydrodynamic performance in rare cases) with ease of construction using developable panels, with superior headroom.

As all the control lines will be lead back to the cockpit, the amount of 'coachroof dancing' will hopefully be minimised, and of course if the boat is at any degree of heel, the curved profile will present one more accessible surface.

For foredeck work, the hatch will be the preferred option, although access over the cabin top will not be too arduous.

 

Can you get the water ballast up under the sheer clamp ?

More effective and it consumes less valuable interior storage space.

Occationally Ill come across a speedy Mac type boat hauling *** .

They always seem to have Bow up trim at speed. Could movable ballast or a trim tab be used to bring the bow back down were it belongs ?

 

Can you get the water ballast up under the sheer clamp ?

More effective and it consumes less valuable interior storage space.

Occationally Ill come across a speedy Mac type boat hauling *** .

They always seem to have Bow up trim at speed. Could movable ballast or a trim tab be used to bring the bow back down were it belongs ?