Long thin hull for motor boat with bulb keel

[Skinnypaul]

Am interested in a design of a long thin motorboat hull (20:1 ratio) using a deep bulb type keel perhaps held by another high ratio aerofoil. I wanted a super stable design but ultra low drag. Can a seasoned mariner explain the downsides please?

 

[TANSL]

If 20:1 is the ratio L/B this boat can't be "super stable"

 

[Skinnypaul]

If 20:1 is the ratio L/B this boat can't be "super stable"

Why? 20ft long 1ft wide 1ft draft 10ft deep bulb keel…

 

[jehardiman]

Why? 20ft long 1ft wide 1ft draft 10ft deep bulb keel…

You wouldn't be able to ride in it, you'd ride on it. There are only a few thing I can think of that need this hull form; enough said.

 

[Skinnypaul]

You wouldn't be able to ride in it, you'd ride on it. There are only a few thing I can think of that need this hull form; enough said.

I was just curious as to why I haven’t seen anything like this. It’s for an autonomous project and I just wanted to know if anyone could tell me why this arrangement wouldn’t be practical. Model yachts and some full scale yachts use this arrangement because they are fast and stable but I’ve never seen a motor boat using these principles.

 

[bajansailor]

Why? 20ft long 1ft wide 1ft draft 10ft deep bulb keel…

Is that 10 ft draft a typing mistake, or is it intentional?

I wanted a super stable design but ultra low drag.

That 10' deep keel is going to blow your drag out the window (and then some!).

If you want your 20' long x 1' wide hull to be stable, convert it into a catamaran.
Or even a trimaran.
Forget about adding a deep keel.

 

[philSweet]

Drag is mostly a surface area issue. Bulbs have a lot of surface area, struts have a lot of surface area, Very slender shapes have a lot of surface area. Double enders like canoes and kayaks can run up to 7:1 It's really only when you go large - as in thousands of tons large and thousands of horsepower large, that skinny begins to make sense because now a much higher proportion of energy is lost to wake and they are trying to go fast.

Keep in mind that for smallish boats in a storm, aero drag and wave impact drag can be five times the hydro drag from friction and wake. So surface area out of the water is also a big problem.

You might look at ocean rowing boats for ideas on hull design. There are some pedal HPV craft as well.

One-of-a-kind pedal-powered "super sea kayak" can be yours for $84,000 https://newatlas.com/within-human-powered-boat-for-sale/22750/

 

[Skinnypaul]

Drag is mostly a surface area issue. Bulbs have a lot of surface area, struts have a lot of surface area, Very slender shapes have a lot of surface area. Double enders like canoes and kayaks can run up to 7:1 It's really only when you go large - as in thousands of tons large and thousands of horsepower large, that skinny begins to make sense because now a much higher proportion of energy is lost to wake and they are trying to go fast.

Keep in mind that for smallish boats in a storm, aero drag and wave impact drag can be five times the hydro drag from friction and wake. So surface area out of the water is also a big problem.

You might look at ocean rowing boats for ideas on hull design. There are some pedal HPV craft as well.

One-of-a-kind pedal-powered "super sea kayak" can be yours for $84,000 https://newatlas.com/within-human-powered-boat-for-sale/22750/

Thanks very much Phil, that’s just the sort of information I was after!

 

[Skinnypaul]

Is that 10 ft draft a typing mistake, or is it intentional?



That 10' deep keel is going to blow your drag out the window (and then some!).

If you want your 20' long x 1' wide hull to be stable, convert it into a catamaran.
Or even a trimaran.
Forget about adding a deep keel.

The keel would be held in place by a super skinny carbon foil to minimise drag

 

[Skinnypaul]

Is that 10 ft draft a typing mistake, or is it intentional?



That 10' deep keel is going to blow your drag out the window (and then some!).

If you want your 20' long x 1' wide hull to be stable, convert it into a catamaran.
Or even a trimaran.
Forget about adding a deep keel.

A catamaran or trimaran would not survive inversion, this hull has to be self righting but remain as vertically stable as possible in most conditions.

 

[mc_rash]

Just wondering, what will be the purpose of this narrow but superstable boat?

 

[sharpii2]

Let's see. At a 20:1 ratio, a 40 foot boat would only be 2 ft wide.

A bulb keel of maybe 2 ft would be more than sufficient. Going deeper only adds more drag.

The only reason for a much deeper keel would be to counter balance something heavy and high up, such as a big antenna or maybe even a sailing rig.

 

[Skinnypaul]

Just wondering, what will be the purpose of this narrow but superstable boat?

In needs to carry a tall antenna array

 

[bajansailor]

In needs to carry a tall antenna array

How tall does this antenna array have to be?
I see that you are in London - where will the boat be located? On a river, or the open sea, or ??
Is it definitely approx 20' long x 1' wide?
And you mention a motor boat, so it will need to have a means of propulsion - a little electric motor perhaps?
Or will it just be moored somewhere?
If you have a motor, then you need batteries and solar panels, and where are they all going to fit on the 1' wide hull?

 

[mc_rash]

If Skinnypaul wants solar propulsion I don't see a reason why it can't be done. 20' × 1' gives a surfacearea about 1,85 m² (yes, sure it will be less) but this might be enough for small electric propulsion?