Max righting moment question

[TeddyDiver]

Originally Posted by Snowpetrel

An inclining test is not done just to verify the calculations, its an integral part of finding the ships actual as built VGC. Once this is obtained for the lightship its fairly easy to generate a fairly acurate GZ curve if you have the lines plans...

If you don't believe me how about a bunch respected Naval Architects
Inclining Experiment - Back Against the Wall? - Boat Design Forums

BR Teddy

[Adelie]

Originally Posted by Eastward ho 24

Looking at the sailboat data site what is a sail area displacement ratio of 13.1, bal/ disp 42.87%, displen 39.63 telling me? I know she's heavy and slow and hopefully safe. I'm in the process of evaluating her design for refitting and capeabilities.

13.1 SA/Disp is rather low, right on the edge of motorsailor territory. Count on motoring a lot. Disp/Len ratio supports this but it is a much less accurate indicator.

Where are you based and where do you want to go?

The R30 can usually be estimated from R1 or R5. Check Skene's out of your local library, it'll have the procedure & math spelled out for you.


A house is but a boat so poorly built and so firmly run aground you would never try to refloat it.

[Snowpetrel]

Originally Posted by TeddyDiver

If you don't believe me how about a bunch respected Naval Architects
Inclining Experiment - Back Against the Wall? - Boat Design Forums

BR Teddy

Teddy, they are talking about required classification society accuracys/ repeatability of 1-2%.

The other issue of Metacentre movement with small angles of heel is true for traditional simplified calculations on slab sided ships. As soon as you get a computer to calculate the actual position of B rather than use the aproximations based from using a fixed value of M the problem goes away.

Interesting about the inclining in air bit.

[Eastward ho 24]

I'm on the Chesapeake hopeing to cruise the Caribbean or where ever the wind takes me.

[Adelie]

Originally Posted by Eastward ho 24

I'm on the Chesapeake hopeing to cruise the Caribbean or where ever the wind takes me.

Are you asking about the EH24 because you found one cheap or because it looks like the dream boat in your head?

SBD.Com says they're built of fiberglass and wood. Is that glass over wood planking or glass hull with wood deck or . . . ?


A house is but a boat so poorly built and so firmly run aground you would never try to refloat it.

[Eastward ho 24]

Im sailing one now it's in really good shape, I just wanted some opinions on the designs seaworthiness. Im living on her and sailing her daily. however I am considering refitting her for extended voyages. I know she's small...but as they say go small go now... I actually was gaining knowledge on some general rigging questions and got a little off topic.

[Eastward ho 24]

And yes the hull solid fiberglass built by ce ryder, the deck is cored in some places and solid fiberglass in others.

[Adelie]

Ok, I didn't read all the way down to the notes like I should have which indicated early construction in wood and later in FG.

Based on length on deck (LOD), beam, displacement and ballast, the boat has a lot of mass committed to "structure", implyings it's pretty strong. Assuming reasonable building techniques its probably plenty strong for offshore.

The only thing I would worry about is the small sail area. I suspect more long term voyage plans flounder on problems with light weather sailing than with heavy weather sailing. If your plan were to travel down the ICW into the Caribbean and back I'd say the boat would work at least acceptably. You will motor the majority of the ICW and in the Caribbean the tradewind sailing would play to your boat's strength.

If you want to move beyond the Caribbean, the very low light wind performance would probably kill your ardor for sailing. If there's a plan to move beyond the Caribbean then you will seriously want to consider a number of alternatives:
1] Replace the boat now. I wouldn't, I'd keep it and use it as your starter boat.
2] Replace the boat when you want to move out of the ICW and Caribbean, by this time will have learned what you want to move on to for a next boat.
3] Replace the mast when you've had your spin down the ICW, thru the Caribbean and back. You would want to add about 7'. Alternatively you could add 5.5', lower and lengthen the boom, and extend the bow sprit by 12-18". There are various tradeoffs but given the high ballast ratio for the boat, any of these options would probably work fine. Both options probably would entail converting to a double spreader rig. Not a big deal. I would also add a removable forestay for a staysail, essentially converting to a cutter. Doing so adds a large number of advantages for single- or double-handing.

For now, I'd take the boat and go for some limited cruise.

As for that being a small boat, I have a Cal20 so you are already doing better than me for creature comforts. Don't let anyone tell you it's not big enough.

[TeddyDiver]

Originally Posted by Snowpetrel

Teddy, they are talking about required classification society accuracys/ repeatability of 1-2%.

The other issue of Metacentre movement with small angles of heel is true for traditional simplified calculations on slab sided ships. As soon as you get a computer to calculate the actual position of B rather than use the aproximations based from using a fixed value of M the problem goes away.

Interesting about the inclining in air bit.

The inaccuraries grow as soon as there's flare, tumbledome or anything which is typical for hull forms typical for boats as does the smaller size. 1 to 2% inaccuracy inquestion was with quite a bit larger vessel.
As you say combined with other data as computerized data we get reliability to the results.

BR Teddy

[Don C L]

Originally Posted by Eastward ho 24

Im sailing one now it's in really good shape, I just wanted some opinions on the designs seaworthiness. Im living on her and sailing her daily. however I am considering refitting her for extended voyages. I know she's small...but as they say go small go now... I actually was gaining knowledge on some general rigging questions and got a little off topic.

Quite a few people have sailed very far in lesser boats. I'd feel quite safe in that design, though I'd like a tad more speed.

[Snowpetrel]

Originally Posted by Eastward ho 24

Im sailing one now it's in really good shape, I just wanted some opinions on the designs seaworthiness. Im living on her and sailing her daily. however I am considering refitting her for extended voyages. I know she's small...but as they say go small go now... I actually was gaining knowledge on some general rigging questions and got a little off topic.

As said by others in this thread, they look from photos to be a pretty seaworthy design for offshore voyaging as long as the construction is sound. Id be worried about the cockpit hatches, but plenty of boats have worse, just make sure they are well sealed and have very good strong latches.

I also worry a bit about the high pilothouse, probably for no good reason. Just needs to be soundly built with a good hatch system and strong windows or lexan shutters over the windows. In a rollover the bouyancy of the pilothouse is a real asset, as long as it stays reasonably watertight.

She might not be tender if the figures are to be believed and the pilothouse and rig isnt overbuilt. Possibly she could sail reasonably well in a bit of breeze.

The logical way to add sail area to this boat is with a long bowsprit. It would be cheap enough to make, prehaps some sort of stainless pipe A frame design. Leave a removable solent stay to the stem for stronger winds with a small hanked on working jib on it. Put the overlength roller furler out to the bowsprit, and get a nice asymetric or drifter to help help her downwind in the light, and a long whisker pole.

[Eastward ho 24]

I'm thinking I'll add a bowsprit this winter and a Solent stay since I think it'll fix the rake in my mast and I could keep my roller and brand new 150 genny. My boom now extends just about to the stern ( I have a boomkin). Boat came with a self tacking jib and a " light air sail(?)" But the po removed it for the roller. if I bumped out the roller onto the bowsprit think I could use the self tacking jib an optional head sail? ( I'm not sure if attaching 2 stays to the top of the mast is correct, then ad a Solent stay and running back stay for a storm sail. However I know this won't gain me more sail area except for the little bit I gain with the bowsprit. Just wondering if using what I already have is worth the effort. But I'll have the mast down soon and ideas are floating

[barnakiel]

I would not add any sail to the boat before actually going sailing on a long cruise and finding out in practice if and when sail area is missing.

Most cruisers start the donkey when it gets light. Bowsprit is just a pita in the marina, docking and anchoring.

Take off with what you have there, add and modify when you find what actually is not working for you.

Do not resolve imaginary challenges that at this point exist just in your visions.

Just make sure all the structure is bulletproof and the boat is dry. Then the rest stems from that.

b.

[TrentePieds]

Quote: " if I bumped out the roller onto the bowsprit..."

Why would you set yourself up for misery??? The roller belongs where the shock loads it must necessarily absorb will transmit to the solid hull - not to a sticky-out bit of flimsy wood or steel tubing.

Bobstay and dolphin striker will brace the sprit against the LIFTING load of the canvas, but there is NO WAY you can brace a sprit sufficiently against the downwards loads of an anchor rode loosing its catenary with a hard jerk!

Using the rigging components you already have, bring her back as close as you can to the original sailplan. She'll sail fine. For a motorsailer. Which is what she is, because that's what she was designed to be. Ye canna change the leopard's spots!

If it's a fast, high-performing racer you want, you've gone up the wrong street.

But take heart: TrentePieds has the precisely same SA/D, though she is, of course, five foot longer on the water line and her design displacement is 9K rather than the 7K of the EH. The Salish Sea, my home waters,+ is not much more than a glorified bathtub, and on some August afternoons you're hard pressed to find even a ripple on the water in the middle of the straits. So it doesn't matter that we're BADLY undercanvassed. So are the boats with an SA/D of 21 :-)

And when it comes up to blow - even a piddling 20Knts - the EH has it all over TrentePieds: The EH is tiller steered rather than wheel steered, which makes her SOO much more tractable. She is full keel rather than fin, she has a real rudder rather than the silly vestigial things that call them selves rudders on modern boats. She will lie decently to her anchor rather than embarrass you in front of every other boat in the anchorage by lurching back and forth like a terrier shaking a rat.

So it's not all bad:-)

But the key to it all is to get her sailplan back to the dimensions that her designer meant them to be.

TrentePieds

[Don C L]

I wholeheartedly agree... don't put the bow roller out on the sprit.