Thread: Will 6" make a difference?

Originally Posted by Aberdeen

Okay, unless convinced otherwise, my next boat building project will be a Hartley 'Flareline' original plan is 14' 6" x 6' 9" and can be increased in length from there. I hope to use my 20HP Honda 4 stroke - (not after speed for this one).

If I was to give her another 6 inches to 15' x 6' 9" do you learned woodies believe this will have much impact on the efficiency of the 20Hp :confused: :confused: :confused:

Aberdeen down south

Aberdeen,

This is another one that needs a bit of research as increasing any one dimension can have some unforseen impacts with the rigidity, performance and general behaviour of a vessel. However, I wouldn't have thought that a 6" increase would be too dramatic.

Hull length generally increases, for a displacement hull, the vessel's maximum speed (v= SQRT Waterline Length x ? (I've forgotten!, but seem to think 7.61??)), but also as the wetted area of the vessel increases, so does the drag at an inverse square.

to reoeat, 14'6" to 15' really shouldn't make that much difference to be concerned about.

Thanks Steve
I tend to agree.
My feeling is that another 6", which is well within the design limitations for stretching this little Hartley, shouldn't really have a major impact on the 20HP, assuming of course that that size o/b would push it along at a comfortable speed. I'm not looking to ski behind it anyway.

Not being a displacement hull I think I'll pass on trying to calculate your technical equation (v= SQRT Waterline Length x ?)

The Flareline is a 15 deg moderate V hull. An older Johnson (2 stroke) 18hp is suggested to move it along at about 32kph. Not sure how the modern 20hp Honda 4 strokes compare.... some think they produce less power than the 2 strokes for the same rating :confused: :confused:

Decisions, decisions.

http://www.hartley-boats.com/flare15.html

Will likely only have a front screen and canopy - might reduce the weight factor a little

Thanks again
Glenn down south

One thing to look at - you're getting horribly close to the length of two sheets of ply scarfed together. If one of those sheets has to go around a long curve, you may start running out of timber. It's not likely, but it's something to have a good look at.

As far as increasing the length goes, Iain Oughtred reckons that increasing any design by 10% will improve it ... but he's talking about a different type of hull so perhaps it doesn't apply here.

Besides which, you're mad ... but we knew that

Richard

Thanks Daddles,
I know I'm mad, proof positive knowing who I have worked for for 35yrs in about 8 weeks time :eek: and married 3 times and starting to build wooden boats at my age instead of wheelchairs.

Although a bit of sanity in that I'm not building alfoil ones! Not all is lost.

Sad thing is the weather, seems my Scotch has evaporated - the bottle is now empty

Madness is just a state of mind anyway......
I need to follow the saying of Alan Alda and find myself
QUOTE:
You have to leave the city of your comfort and go into the wilderness of your intuition.
What you'll discover will be wonderful.
What you'll discover is yourself.

Richard,
A valid point re the ply.
It did cross my mind and at a rough estimate 2 sheets should be okay - being a cautious person who hates waste, my 'skeleton' will be screwed together first before the expoxy is applied. This will also let me check to see if I will get away with two sheets. If not it is then just a minor adjustment on the building stock to bring it back closer to the original dimension.........

I know, more time/work but better than having to fit a 2" bit at the end

Also being a 'straight' guy I'm not into scarfes, prefer a nice tight butt joint.

You need to have a look at the butt joints on Rusty, then have a look at the scarf joints on my Yellowtail. They aren't hard and are less work than some of the things you did on Rusty - well within your own personal psychosis when it comes to building

Richard

Okay Richard
You've seen my butt joints, will pop over sometime and check out your scarfes