Modifyng the beaching keel

[fallguy]

I have a beaching keel with a sacrificial timber made of laminated ash timber and a laminate of 600/225 glass over it. It is about 35mm thick.

The boat attains speeds of 20 knots.

Would anyone be willing to recommend changes to the leading edge shape? After I put it on, wondering if the shape is too blunt.

This picture is from the starboard side looking aft, so you see the leading edge of the timber.

 

[bajansailor]

That is a rather bluff frontal area for sure, which is not doing much good re beaching, and if you happen to (eg) run over a floating log at speed, it will still get clobbered quite hard.
Could you cut out a wedge going back almost as far as to where the keel is rising off the ground?

Edit - re your other thread about adding bulbous bows -
Composite bulbous bows https://www.boatdesign.net/threads/composite-bulbous-bows.67969/
maybe the beaching keels could be faired into the new bows, if the new bows will reach as far aft as where the keels start?

 

[jehardiman]

I'd just round the sides in with the near same shape as the profile. You do not want the leading edge too delicate, otherwise you will just rip the whole thing off.

Also, unless the skeg is also used for lateral force, rounding the edges over to ~10% of thickness will greatly reduce drag.

 

[fallguy]

I'd just round the sides in with the near same shape as the profile. You do not want the leading edge too delicate, otherwise you will just rip the whole thing off.

Also, unless the skeg is also used for lateral force, rounding the edges over to ~10% of thickness will greatly reduce drag.

Do you mean the entire edge? It is glassed with 1708 on sides and bottom; I could round over, but I'd be hogging glass and would need to do it with the boat lifted.

Maybe best to just hand grind the front leading edges for now.

Also wondered if a vee front would be better.

Thanks, much appreciated.

 

[fallguy]

That is a rather bluff frontal area for sure, which is not doing much good re beaching, and if you happen to (eg) run over a floating log at speed, it will still get clobbered quite hard.
Could you cut out a wedge going back almost as far as to where the keel is rising off the ground?

Edit - re your other thread about adding bulbous bows -
Composite bulbous bows https://www.boatdesign.net/threads/composite-bulbous-bows.67969/
maybe the beaching keels could be faired into the new bows, if the new bows will reach as far aft as where the keels start?

perhaps...the bulbous bows also need to be able to hit the beach

 

[Alan Cattelliot]

Hi,

judging just by eye, and according to the approximative thickness given (35mm), the width could be about 50mm. I picture something like this :

The flow is influenced by the 20deg angle. It is sufficient for lines or rope not to get stucked, although, from an hydrodynamic point of view, you could get a little improvement in setting a greater angle.
Could made out of a piece of solid wood, cut and rounded. Delaminate the existing keel and the hull over a 50mm width band, shape cut, epoxy glue, re-laminate.

Don't know exactly the drag reduction, but the flow will certainly be cleaner, and the lines & ropes risk is also diminished.

 

[fallguy]

@Alan Cattelliot

The width is about 100mm or maybe 90mm.

I really like the idea of adding a piece.

But Hardiman suggesting rounding the outer edges..why did you not consider?

 

[Alan Cattelliot]

If the width is greater, then the improvement with a piece of wood in front will be even better.

The idea of Jehardiman of rounding the outer edges is also good, but this is a hard work, since the piece is laminated with GRP.

Also, the idea of making a Vee front is nice, but then it is possible that the boat could just be blocked more often when beaching.

These keel outfits do protect the hull when beaching and, like skis, helps the boat sliding over the sand grain. In the near where I live, the continental shelf extends more than 600miles from the cost line. Tides are strong, and Fisher man do have these kind of keel protection, allowing also the boat to be towed by tractors when there is no water.

 

[fallguy]

If the width is greater, then the improvement with a piece of wood in front will be even better.

The idea of Jehardiman of rounding the outer edges is also good, but this is a hard work, since the piece is laminated with GRP.

Also, the idea of making a Vee front is nice, but then it is possible that the boat could just be blocked more often when beaching.

But if adding a piece, I can do whatever I want.

Sorry, 'blocked more often'?

 

[Alan Cattelliot]

But if adding a piece, I can do whatever I want.

Sorry, 'blocked more often'?

Stucked in the sand. Does it make sense ? A Vee will let the surface penetrate the sand, while a ski-front shape will raise the boat over the sand, making her towing more easy.

 

[fallguy]

Ahh. Okay. Thanks. It will be fun trying to make the BB and the existing keel work well in concert..

 

[seasquirt]

Hi fallguy, what I'd do with your beaching keel, (if it was mine), I'd leave about a centimetre thick of the sacrificial timber at the leading edge, so you don't have a thin leading edge. You can fillet it with a small wedge or thickened epoxy, to improve flow over it. Then take a cut back from there, (1cm down), at about 60 degrees or a bit more, to ease that resistant shape. Round everything substantially going back to the parallel part of the keel, then re-glass.
A vertical Vee shape presents a narrow edge more prone to damage to its coatings if struck, will take direct bumps and grinding at its bottom corner, is easier to bury in shallows like a plough, and isn't the smoothest shape for water flow.

Maybe do nothing and think about it while you make your re-modeled bows, and then see how it all looks together. It's not a critical modification and can be done any time the boat is dry. A new solution may present itself, and you haven't wasted effort on something that was later changed again.

 

[Alan Cattelliot]

Ahh. Okay. Thanks. It will be fun trying to make the BB and the existing keel work well in concert..

Yep, small touch, big fun. Catamarans are such nice boats.

 

[Milehog]

Not sure if you are aware of jehardiman's bona fides but I'd consider his advice on shape. Look at the fronts of modern, aerodynamic cars. The slippery shape is not just in the profile but the plan as well.