sailboat bows

Thanks Fast Fred, where abouts in Conn. I grew up there,currently in southern Maine

 

Just for grins. Here are a couple of 33'ers. Very basic, down and dirty stuff. They're actually quite slack bilged. One with 5' freeboard at the bow and one that is 4'.

The higher freeboard makes the vessel look shorter. More like something in the 20' range. I'd be concerned about windage on such a boat. I don't know that you would gain much in the dryness area either.

I'd go to the marina or go to some manufacturers websites and get some actual figures off of some boats of that size to see how close or how far you would be from some production boats.

Oh, these were done with FREE!ship.

Goodluck

 

Thanks learpilot, my design has a more pronounced sheer than those, almost a Maine lobsterboat sheer, I live in Maine. I've been to the boat yards and the manufacturers websites, know something, they all look the same, guess I'll just trust my instincts.

 

Chandler,

New thread, "Lobster"

 

When motorsailing , or punching into the waves , a 4 ft freeboard will take water over the bow at 4ft 1 inch of imersion.

A 5 ft bow will begin to have grean seas after 5ft 1 inch.

The difference is extreme as much more hull must be immersed to get the slopy seas sweaping aboard.

Its a foot extra of BOAT that must be immersed.

FAST FRED

 

Great question! What you're referring to is often called a plumb bow (or vertical bow). Unlike traditional raked bows that angle back, a plumb bow drops nearly straight down to the waterline, and yes—increased waterline length is a major reason. But there’s more to it than just that.
While the plumb bow design might feel unfamiliar and not as intuitive as more sloped bows, it’s primarily about improving performance—especially speed and efficiency. For most recreational sailors, this isn’t as critical, but for racers and performance-oriented cruisers, it's a key design feature.

If you’re considering a boat with this feature, keep in mind how it might handle in different sea conditions and what your primary sailing goals are!

 

Well….define efficiency and performance! . Arguably the vertical stem is only more efficient and faster if a boat is measured by LOA, often ignoring bow fittings.

Increased waterline length, if nothing else changes, normally implicitly increases wetted surface so, all else being equal, often makes a boat slower in flat water or downwind in light airs. A plumb bow can also be a complete PITA for a performance cruiser because it can encourage the anchor chain and anchor to hit the bow when in light winds or handling the anchor. To “solve” that problem many boats now have longer bow fittings - but why fabricate and bolt on a oversized bow roller when you could just rake the bow itself?

If you take a fixed waterline length and added a raked overhanging bow you inherently increase deck space, forecabin space and often improve anchor handling at fairly low cost, so is that more or less efficient than taking the same fixed waterline length and having a vertical stem?

It’s interesting that US sailors seem, from what I can see, to be more into perceiving vertical bows as being efficient and cool than Brits and Australians. I wonder whether that’s because many more British and Australian sailors grew up sailing dinghies in a scene where early classes were limited by LOA and therefore had vertical bows. Because we grew up with them, we don’t see them as something new and cool. Meanwhile US and Euro sailors grew up in OD classes that had raked bows (because they are so practical and logical) and therefore see vertical stems as new and cool.

It’s interesting that when great skiff designers like Julian Bethwaite, Bieker and Morrison design very successful production skiffs and boats like the RS400 and 200 and 29er and 49er, they all dump the vertical bows they use in similar restricted-length classes, and instead go for overhanging bows. Great skiff designers don’t do that to make their boats slower or less efficient. As people from G L Watson to skiff designers have noted, if you simply draw out the lines of a normal fast midships section to their logical and fair conclusions, you inherently end up with an overhanging bow. A vertical bow actually requires distortion of the hull lines from the normal flared midships.

 

The vertical bows on the early NACRA catamarans was all the rage at one time,....and admittedly you could could stuff those bows with less tendency to pitch pole the boat,....BUT you had to make the decks of those bows very slim. On a cruising cat those slim bows produce numerous problems with docking, anchoring etc, etc

 

Ram bows do look hot though

 

Obviously, the stems on the bow of sailboats are vertical due to the length limits, exactly as has happened to the mainsails

(And as always happens, people copy and imitate, for example MainSails, without knowing what they are copying)



This yacht capsized three times while trying to Surf when it tripped over itself.

Let's look at the pieces of this typical disaster (created by the typical standard troglodyte designer) in this bewildering industry that respects neither science, nor experience, nor tradition

1) There is a longitudinal mismatch between the position of the yacht's center of Gravity and the center of Flotation, such that the force of the wave, the Froude-Krylov Force, has a significant leverage in conjunction with the powerful force of the Earth



(tested fully submerged in a towing tank. Hörner, Fluid Dynamic Lift)

2) The bow dips a few degrees, and its sharp shape with very vertical topsides, plus the Forefoot, creates a low aspect ratio wing that produces a significant Lateral force when the heel breaks the symmetry of the hull

Now look at This



First) the First important question is hidden: longitudinal Balance: longitudinal position of Center of Flotation= longitudinal position of Center of Bouyancy

Second) that bow produces little Lateral force, and ... produces Vertical High pressure, hydroDynamic Lift (and the Stern produces Vertical Low pressure: Suction)

A magnificent SurfBoard

 

Ultramodern 1-ton WindSurf Board respectful of science, experience, and tradition, Thomas Harrison Butler in Memoriam

(still 'photo' around 0.60 Froude number)

1) hydroDynamic Lift > 3000 Newtons

CF: Longitudinal position of Center of Flotation (due to "heavy quarters" and very Wide Transom)

CG: Center of Gravity
2) Almighty Force of the Earth

3) hydroStatic Force

4) hydroDynamic Suction ca. 1000 Newtons



Rr DELFT: prof. Lex Keuning: 8.9%
Rr Surf Model: 9%