Effects of racing rules on boats

Vertical stem long before racing rules or tonnage rules etc?

 

I think you wrong about racing those, they race in war!

 

Or maybe they where racing to the fishing grounds and back?
But no rules I think!

 

How does one 'fill in' a raked bow, and keep the flare that creates the drier ride? And of course, the toe of a plumb bow is more likely to dig in or catch waves, and make steering difficult. In a sharpie, that's dealt with by raising the foot of the stem above the waterline....which isn't always practical in other designs, or effective in rough water anyway.

I don't think you can reasonably dig in and dogmatically claim that the only advantage of a raked, spoon or clipper bow over a plumb bow is an artificial one, as a LWL rule cheater for ratings.

 

Filling in the bow overhang also moves the longitudinal center of flotation forward and decreases the rate of change of reserve buoyancy as the bow immerses. This combination could result in a less dry ride, particularly if the boat is relatively heavy with a deep forefoot.

 

The first thing we should do is make sure we are using the same terms. Most modern boats, even those with raked stems, do not have flare (or flair if you prefer) in the bow sections. They are generally straight lines, or even with flam. Most spoon bows have flam, not flare (flair).

As I showed with the I14 linesplans earlier in the thread you can have flare (flair) in a plumb stem design if you so desire.

I'm wondering where this discussion of "dry" ride comes from? Can you explain where the wetness is coming from and on what points of sail? I can better address your concern if I know what you are talking about.

There is no evidence of this claim at all. A plumb bow with a shallow forefoot would probably have less tendency toward this issue than a raked stem with a deep forefoot (mid-70's IOR type).

 

It is all rather mute, question of the perspective - you begin by watching at the boat with a vertical stem and stern and thinking if I just add few feet at the front and the back I’ll get more boat for the same WLL with reserve volume in the air to help part the seas e.c.t. … (as in my drawing nr. 1).(rough sketch in the pdf attachement).

I begin as in drawing nr. 2 & 3 – I look at the overhangs and think it is a shame that all that volume in the front and back just floats in the air doing nothing most of the time, just adding weight at the wrong places and making for the weaker structure. Better stretch the waterline all the way making it (almost) equal with a deck length. Add a volume at the waterline where it can do some good.

There are a lot of benefits to gain, I think. 10 or 15 % longer waterline means significant drop in the displacement/ waterline length ratio. Longitudinal stability grows exponentially reducing pitching a lot. Entry - angle is much sharper reducing wave making resistance and reducing bow wave hight. Same displacement spread on the longer waterline means straighter run and a bit shallower, flatter bottom of the boat. That reduces draft a bit and makes efficienter end plate for the fin keel. Rudder is further to the stern, longer moment increasing steering force.

All of that would lead to the considerable faster boat in most of the circumstances, easier to steer and better behaved in the seaway because of the reduced pitching. Boat would be also faster and more fuel efficient under power.

Everything comes at the price of course, the only two disadvantages I can see are:
-difficulties with anchor handling as Troy rightly pointed. (Short bowsprit necessary).
-a bit slower in very light airs because of bigger wetted area

 

When I say "filling" I am not so much being literal. Starting with a blank sheet of paper a plumb bow design is of course not simply a raked bow design with the bow "filled".

In my experience the plumb bow style with additional reserve buoyancy forward is actually drier off the wind, since the bow does not depress as much as a raked bow. However, this is an observation not based on good control since I have not seen two similar boats with the different bows performing side by side.


I don't think many modern designs would combine a plumb bow with a deep forefoot.

 

I agree. And I think the modern plumb bow designs generally are an improvement over earlier raked bow designs. Without rating rule constraints the "ideal" sailboat boat bow is probably a vertical stem with a slight knuckle just above the waterline.

 

One nice example:

 

If you want to hove to, better having a deep forefoot.
Every design is good if it is designed for the purpose intended.
No rule can be dictated for all the sail boat, it is simply impossible, or the customer suffers by the lake of integrity of the designer. The shoe fits all type.
Some time shear ignorance of history and been influenced by the trend dictate what the designers draw.
Daniel

 

What I think is really funny is that a discussion that was intended to discuss the effects of rules on boat design so quickly created a new rule by which to measure boats.

The reality is that ALL boats are compromises, and the important question is what design criteria you concern yourself with.

If a racing rule penalizes water line length but allows free overall length you get boats that look like a Columbia 50' with 17 combined feet of overhangs. As soon at the boat heels over 15 degrees of course she has a waterline of 45'.

If a rule penalizes overall length and ignores WL then you see plumb ends to provide the fastest sailing for a given length.





Now the issue at hand... I think there is some confusion that only 'rules' created by rating bodys have effect on boat design, while in reality every owner creases his own set of rules, and buys a boat to meet those specific criteria. The only difference is that racers have gotten together collectively to tell the manufacturers what they want while cruisers are less organzed. While a cruiser may not consider their boat criteria a 'rule' like a rating body does, it has the same effect. Cruisers these days have passes a rule that a cruising boat over 50' must have a generator and AC so the boats are designed with them in place. Those boats that doesn't have them are penalized by no-one buying them.

 

Milan
You are drawing static waterlines, sketch in the dynamic waterlines and you'll see a different picture.

 

Why should it ? That just makes the discussion subjective again, and makes length on deck the limiting factor.

In pitching characteristics there is better longitudinal stability and damping with a raked stem and flare since damping is greater with a higher rate of change of immersed volume.

If you introduce exaggerated flare with a plumb stem then you'll have a greater wave resistance. At the top of the stem it will be quite bluff and you also create a diving plane.

More reserve buoyancy than a much smaller waterline boat yes, but these are not helpful generalizations. Once again you are looking at the design holding either deck length or waterline length constant.

Think of a raked stem as a means of providing a fine entry with a reserve buoyancy tank, a longer dynamic waterline and a good damping mechanism for little extra cost in materials. For cruising boats the raked stem can add other benefits as well as already mentioned.

It might help to get away from small sailing vessels and look at motor vessels under 70 feet and consider why the optimal designs are different. Consider a modern vessel that’s designed to go out or stay out in rough weather, look at the bowshape.

Here’s a useful exercise, trim the boat to 15 degrees bow down to simulate running into a wave and look at the waterplane area relative to the CoB. If they are far apart then you are inducing a dynamic pitching moment. You’d design the hull shape cope with the range of expected conditions and the desired vessel response.

Plumb stems in cruising boats are something of a current fad, that doesn’t mean they are poor designs, but by the same token there’s nothing wrong with overhangs either. If I had one I’d want a long bowsprit for anchor handling, and then I may as well have a bit of deck there and then I could lash a couple of 44 gallon drums to the bowsprit to stop her plunging …..

 

Dynamic waterlines change situation somewhat, but I think that boat with a longer waterline, spreadout displacement, flatter run would still pitch less and sail faster.

Not exactly modern, but she would be my choice of small motor vessel to stay out in rough weather. (Not much overhang).