Tapered chine width

[Nojjan]

I would like hear your take on the chine shape/layout in the attached document. What are positive and negative aspects to a tapered chine width (not a tapered chine) on a otherwise monohedron hull.

[USCGRET/E8]

I think it depends on the use of the boat. My Airboat has these and it works out just fine!

[tom28571]

I use chines like that but they are at least double the amount of taper shown. On a monohedron hull, the taper also results in a positive angle of attack for the chines relative to the aft hull bottom. This will get the boat up on plane quicker at a lower speed than otherwise by lifting the stern but will also depress the bow. This can be a positive or a negative depending on the intended use and speed objective for the boat.

[Nojjan]

Interesting input Tom

When you say double the amount of taper, do you mean that the ratio "chine-width-transom"/"chine-width-midship" is even more than I have drawn?

Also, can it be so that at higher speeds the positive angle of attack is eliminated by the hull lifting enough not to be affected by the chine? Say by using lift rails on the hull surface.

Thanks / Jon

[lazeyjack]

Originally Posted by Nojjan

I would like hear your take on the chine shape/layout in the attached document. What are positive and negative aspects to a tapered chine width (not a tapered chine) on a otherwise monohedron hull.

to mwe the width looks ok, but it is far from monohydron

[Nojjan]

Originally Posted by lazeyjack

to mwe the width looks ok, but it is far from monohydron

Well, actually it is monohedron as far as I understand the term (constant deadrise). To be more precise it is "delta conic with tapred chine width". The reason that it does not look monohedron is that the chine varies in width which makes the hull seem warped when it is not.

Best regards / Jon

[lazeyjack]

sorry jon, dont see it, here are to monos I built, both with chiines 160 or so wide aft to 30 wide at stem

[Nojjan]

Nice boats Jack

I especially like the one on the second pic.

I have also attached a second sketch including waterlines on the hull. Straight and parallel waterlines dictates that the surface is flat (single plane) thus monohedron as I understand it. But maybe I have missunderstood the meaning of the term?

Best regards / Jon

[diagram]

Nojjan,

I think you need to look at your buttocks. Incresing the chine flat will increase your deadrise as you go aft. Sloping the chine down in profile can compensate for this but I imagine you will have to put some time into your model to do this. What software are you using?

[Nojjan]

These discussions are fun, and also the reason why I posted the question. The possitive angled chine on an otherwise monohedron surface (constant deadrise) produces a tapered width, or if you may, the other way around. I have added yet another sketch with all three views (sorry for the european placement). In this you can see that the waterlines are straight and parallel and so are the buttocks (over the aft part of the hull). The surface is truly flat according to both the softwares I am using (SolidWorks for parametric modeling and Rhino for stability and some other analysis).

Best regards / Jon

[Nojjan]

I just noticed that my PDF printer is making some lines bend (strange !). I will try to post a picture of the last document instead.

[Nojjan]

See attached for alternative to "tapred chine width 3".

[diagram]

That looks good - I have noticed that nurb surfaces can distort like that - sometimes printer sometimes me. I don't really use solids so I don't know. Try the "zebra" function in Rhino - in case you don't do so already. Helpful for checking fairness.
Is the boat designed for Outboard/Sterndrive or Inboard? The reason I ask is that I usually see the style you have chosen for Inboard designs. From about Sta.6 aft close down the chine - loosing some volume aft is usually advantageous for your LCG placement and the flat helps out of the hole. Somewhere I probably have a percentage for a guideline on closing down chine in plan view. OB's/Sterndrives often need that volume aft for LCG. What is your Pristmatic and LCB. Don't mean to be nosey - I am big on planing hulls.
Best,
Diagram

[Nojjan]

Don't worry about being nosy, I am the same way. Cp about 82% and LCB about 6.8ft.
My real problem is to increase stability but still maintain a fine entry and reasonably high deadrise for operation in semi-open waters. The main particulars are LOA 22.1ft, BOA 7.4ft, 3700 lb max load (3000 lb avg), 22 deg deadrise at transom, sterndrive diesel engine (VP D3-190hp WOT at about 39-40knots).
/J

[RANCHI OTTO]

REFOLO ASD

Length > 6.20 m
Breadth at transom > 2.42 m
Deadrise > 22 deg.

Power > 1 x 225 hp DP Volvo
Speed > 45 knots