I need a naval architect please

[Geno67]

Thanks banjasailor - you r inputs were pretty much spot on. I made a few changes based on measured distances for distance from transom and guesstimated distances for vertical.

 

[gonzo]

@bajansailor: Are you measuring the vertical distance from the waterline?

 

[bajansailor]

@bajansailor: Are you measuring the vertical distance from the waterline?

I was just roughly estimating from the keel, using a roughly assumed hull depth.

 

[Geno67]

If I do a hardtop like this - except it will be a continuation of the vertical hull sides for the supports for and aft - as long as I keep it centered for and aft, it shouldn't change the LCG?

It too will be very lightly built. 1/4" ply top with 6 oz glass. Vertical supports will be 5/16 ply with 12 oz glass. A few hoops across the bottom that are steam bent 3/4 x 3/4. Peel ply used everywhere there is glass to keep epoxy amounts used as low as possible and to prevent sanding on the flat(ish) parts.

Or should I just use a bimini same as I always have to keep the sun and rain off?

 

[Geno67]

I was just roughly estimating from the keel, using a roughly assumed hull depth.

I am carrying the standard inverted v through all the way from 54" from the bow to the transom. I have settled on no chines, and +0.5' vertical distance from the outside bottom corners on the centerline. I'll have an elongated dihedral splitter that matches the vertical distance from the outside about 5" wide that will go forward 30" or so along the centerline in front of the transom.

 

[bajansailor]

Re the hard top in your photo above - if you do decide to build one on your sled, include it as well in your weight estimate (which will be a lot more detailed and accurate than my rough estimates above).
You mention a 'few hoops across the bottom' - are these laminated from timber, going transversely across the cockpit?
If they are not, then be aware of transverse racking loads on the hard top, eg if somebody presses sideways on it, what is resisting it from flexing? .

 

[Geno67]

Are you saying you think a hardtop would be better than a bimini? You didn't answer that question - lol.

Transverse loads would be handled by tying it into a frame for and aft is the only way I would think it could be properly built. Carry the same 2" up about halfway and then taper down to 1" at the top. Lean those two bulkheads for and aft as needed. Rear leaned for to match roughly the centerline of the outside hull vertical extension, fore leaned aft to match the angle of the windscreen. With some big ole cutouts in the aft upright to save weight.

 

[bajansailor]

Biminis and hard tops each have their own pros and cons - I think you have to make the decision yourself as to which one you would prefer.

Re transverse loads, a typical bimini framework (eg made from S/S tube) has very little resistance to sideways loads.
A hard top would have more resistance, especially if you lean the legs inboard a bit, to try to resist sideways racking.
You might still need to incorporate some form of bracket connecting the roof to the side supports.
And there will be potentially large loads in way of where the side supports are attached to the side decks.

 

[DogCavalry]

I definitely require a hard top on Serenity, and the new 18'*7' commuter will have a hard top as well.

What do you mean by no chines? No non-tripping chines?

 

[Geno67]

A bimini would save on weight and aerodynamic drag at times. I generally launch 45 minutes before daylight and run as fast as I comfortably can for the first few hours. Once the sun gets high enough to warm us up, I raise it and leave it until the sun gets low enough to shine under it.

It would also help with top speed runs as I can lay it down when I want to see what she can do. In a straight line. I'm not a big turn sharp at speed kind of guy.

 

[Geno67]

I definitely require a hard top on Serenity, and the new 18'*7' commuter will have a hard top as well.

What do you mean by no chines? No non-tripping chines?

Yes sir. I slow down to almost idle speed to make all but the most gentle turns. Leftovers from my military days in a 21' inflatable with a chrysler 70.

 

[DogCavalry]

Understood. I remember slapping the helmet off a guy for saying "copy".

It's your call. Serenity can turn almost in her own length. A moderate increase in building complexity.

 

[Geno67]

one delta ten tango

I may add them back in. I'm still 2-3 months from even being where I can start.

 

[Geno67]

Understood. I remember slapping the helmet off a guy for saying "copy".

It's your call. Serenity can turn almost in her own length. A moderate increase in building complexity.

I forget - was your chine a simple one or did it get wider and slide under then get narrower and slide back out? I'm drawing the 4th or 5th iteration of the hull and would prefer to just put a simple uniform width and angle chine under there most of the way.

 

[DogCavalry]

It was 10% of beam at each side of the transom. 24° if Iirc. Rolled up gradually but maintained the same width of material, so % Of beam decreases. It's basically very similar to the TX 18, without the bizarre inclusion of rocker. Bottom chines exactly parallel.