Following Seas Dangers?

[UNCIVILIZED]

To give you an example of what I described, take a look at the below 2 catamarans by John Shuttleworth. Pretty much, the (newer) 37'er is a variant of his older 35' catamaran with reverse bows added onto the smaller design.
Shuttleworth Design - Shuttle 37
Shuttleworth Design - TEKTRON 35

I can't say that I've read this thread in it's entirety, but... People's natural inclination is to want to keep their speed down in waves, especially when they're out in waves that are both large & overtaking. This can however, be a deadly mistake. Here's why.

When you're sailing downwind, in the direction the waves are traveling, so long as you're not surfing down the face of one, the water flow over your rudder is in the conventional direction. Moving from forward to stern.
But then, as the boat's overtaken by the wave, & wave speed matches or approximates boat speed, then little to no water is flowing over the rudder in either direction. So that when that's occurring, even if you turned the rudder 40 deg. one way or the other, little would happen, as it's in water that's stationary relative to the boat. Which, of course can be fairly dangerous, especially when you begin your initial descent down the wave's face. Assuming, that is, that you don't slide off of the back of the wave.

Either way, whether you surf down it's face, or slide down it's backside, you need to have water flowing past the rudder in order for the helm to answer. Which, boat speed is the key to this. And the higher a boat's speed, the more water flowing past the rudder. Plus the higher the boatspeed, the shorter the interval of time when you & the wave will be moving at about the same speed. So don't overdo the slowing the boat down thing too much. It can be mongo dangerous, even though it feels safer except for those brief seconds when the helm doesn't answer. Those same seconds where you have zero control as to whether or not the wave fully turns you sideways, thus leaving you ripe for bowling over by the next big one, now set to strike you fully beam on.

[Mr B]

I would tend to say the Shuttle 37 would have a tendency to sink the bows,
Its not a design I would like to sail in, But thats only my 2 cents worth,

[UNCIVILIZED]

Originally Posted by Mr B

I would tend to say the Shuttle 37 would have a tendency to sink the bows,
Its not a design I would like to sail in, But thats only my 2 cents worth,

If you look closely at the drawing of the 37' from overhead, you can see where the reverse bows are drawn via dotted lines. Drawn on in front of, & below the lines which represent the bows at deck level. And the bows at deck level are those of the 35' boat. Such that the 37' is merely a 35' with extended, reverse bows added onto the bows of the 35'.
So that basically, the bows of the 37' have the same buoyancy as those of the 35'. And all of the accomodations, rig, etc. of the 35' are the same, & in the same exact location on the 37' (but for the bow extensions).
Make sense?

And yes, I'm with you. The bows of the 37' don't give one a warm fuzzy feeling. The even spookier thing being how some of Shuttleworth's boats sail. Since the 35' is an overgrown version of his 31'er, who's bows dip too much for my comfort just in moderate weather.

https://www.youtube.com/watch?v=am6YTSVZH0A

[Mr B]

Warm Fuzzy Feeling, hahahahahahaha I like that, Its hilarious,

[beiland]

Here is one of those 'reverse bows' I was speaking of



Dazcat D1495 Catamaran Yacht - Nominated European Yacht of The Year 2016

[Mr B]

That goes against all my Engineering principles,
There is no lift in the shape to make the boat lift itself up to go over the water,
Not through it,
Its more likely to nose dive with that shape,
The bow looks like its always facing down as well,
They must be happy with it, It works for them,

[UNCIVILIZED]

Yep, those are what I was referring to. Nice boat! If she spooks the owner or crew too much I'll give'em $5 for her. Aw heck, $5 & a nice bottle of champagne... with which to christen their replacement for her

[Steve Bean]

Has anybody here ever tried oil on the water? Google "The use of oil to lessen the dangerous effect of heavy seas."

[Cheechako]

Bow digging in was always something I wondered about on Cats. Most cats are a length to width ratio of 2:1. On land vehicles the closer you get to 1:1 is a recipe for disaster/overturning. One wonders if so on the water. Yet, I don't hear much of an issue with that on cats. Although memory says there is a video of one racing cat digging a bow in and doing just that...?

[UNCIVILIZED]

Originally Posted by Steve Bean

Has anybody here ever tried oil on the water? Google "The use of oil to lessen the dangerous effect of heavy seas."

In conditions such as are being discussed, you'd simply wind up leaving a trail of oil in your wake. As you're moving downwind at high speeds. Whereas the kind of thing you're referring to is for when you're hove to. At least that's what my memeory's telling me.

Originally Posted by Cheechako

Bow digging in was always something I wondered about on Cats. Most cats are a length to width ratio of 2:1. On land vehicles the closer you get to 1:1 is a recipe for disaster/overturning. One wonders if so on the water. Yet, I don't hear much of an issue with that on cats. Although memory says there is a video of one racing cat digging a bow in and doing just that...?

Cat's/multi's can & do flip along the diagonal in such circumstances. As the windward hull will already be wanting to lift, & then the leeward bow buries. As this occurs, the wind pressure on the sail takes a big jump, thus pushing the boat over & forward even more. So that the windward transom lifts out of the water, & tries to trade places with the leeward bow. Though the leeward bow will often enough dig in sufficiently during this so that the capsize is oriented more in the transverse direction. But any way you cut it, it's a cartwheel gone very, very wrong.

Do a search under "Ask Dr. Crash". There are some wild, & hilarious wipeouts from his Sailing World magazine column. Sailing World Dr. Crash - Bing images

Also, if you do some digging around on John Shuttleworth, the designer's website, he discusses this stuff. Shuttleworth Design - Articles

[beiland]

I believe the trend in reverse bows really got started with the NACRA (images) 'beach cats' back in the early/mid 70's. Their's was a plumb bow with a volume of displacement down below the waterline, and very small deck area up top. The basic idea was that this bow could be pushed THRU the waves with less resistance, and if the deck got submerged beneath the wave the smaller area of that deck would resist getting really pushed down hard,...it could pop back up quicker.

The somewhere along the line someone else decided that the 'excess' deck area could be further reduced by raking that plumb bow back into a reverse form.

Sure these bows do work for performance oriented cats, but they can be objectionable on cruising vessels, ie: image working on one of these 'platforms' during docking maneuvers, or how about anchoring, and anchor line fouling, or incorporating some sort of rubrail into the design,...or as I have questioned on this subject thread,...racing down the slope of a BIG following sea???

And BTW its those BIG mainsails that contribute a lot drive to push those bows under, particularly off the wind. Have you noticed how many of the big ocean racing multihulls from France are all moving their whole sailing rigs rearward.

[ardoin]

I hate the phrase "fair winds and following seas!" People who say that have never been in following seas! Fine at 6 to 10 ft, not fun above 16 ft. And I've never had fair winds with a 16+ft following seas.