Plumb Stems

[DougC]

Have been looking over lines of various boats and I'm trying to figure out what effect a plumb vs. a raking stem has on a boat's handling. I can guess at the the advantages of each by comparing boat types with distinctively different stems (e.g. whitehalls vs. dories) but don't quite get the mechanics. Anyone feel like venturing an explanation??
Doug

[Ian McColgin]

There may be factors other than plumb v overhang to consider.

First, divide between above the water and below.

Below the water: A fine entry, maybe a little hollow to the waterlines, is nice if the beam to length ratio allows, assuming that you're looking at displacement speeds. All sorts of other considerations if you're into a planing craft, which it sounds like you're not.

But still below the water, many power boats and row boats have a fairly deep forefoot while sailboats often have a cutaway forefoot. Sail boats can't have too much of their underwater lateral resistance foreward (except what we genericly call dhows) or they will gripe a bit and be very hard to sail off the wind. A row boat too deep in the bow and too little in the way of skeg will also gripe and be hard to row.

Moving above the water: Your goals are to carry the deck you want. The bow gives bouyance over waves, so choises are dictated by use and waters. A very fine bow above the water line will not rise with waves, but may slice through them very nicely if the waves are not too large.

A plumb bow above the water lends itself to being quite fine and the whole 'plank on edge' approach to design proceeds on the theory that it's better to go through a wave than over it.

A nice overhang to the bow gives you some extra bouyance as you need it either rising with a wave or gaining hull power as the boat heels.

Done right, this leaves a shorter water line and less surface area resistance in calm sailing . . .

Extreems, like the yawl Hutoka from before WWI, that has about 55' LOD on a 28' water line, are simply flat water rule beaters from the day when the waterline length was the most important handicap feature.

Anyhow, looking at cruising sail boat trends, the old CCA handicap encouraged nice moderate overhangs like the Hinkley Pilot 35 and any number of other nice S&S designs. The older version - pre WWII Aldens - also tended towards nice moderate overhangs. The IOR rule seems to favor pinched ends and no overhang.

Lots of choises. Look to total design harmoney.

G'luck

[John E Hardiman]

One more thing about plumb stems and overhangs. You see more plumb stems on working boats, and more overhangs on yachts.

Working boats were taxed and payed fees on their tonnage (length on deck * maximum beam * depth of the hold /(93 to 100, depending on when and where you are)). So an overhang didn't gain you much except more taxes and fees

Yachts, on the other hand (after about 1870), were rated by length on water line. As the overhangs increase heeled waterline, the boats sails as a longer length in a shorter class.

[JimD]

Not an explanation, but John Vigor, author of "The Seaworthy Offshore Sailboat" says "Long overhangs work well in calm water, but short overhangs-even absolutely plumb bows and sterns-are safer at sea."

[DougC]

Thanks for the info. Answers my questions and then some. More ??? to follow . . .
DC

[paladin]

Straight lines are easier to cut with a skil saw.... :D :D

[ACB]

Be cautious about plumb stems in smallish seagoing sailing boats. Unless the bow has a lot of flam in the topsides, she will pitch excessively and if severely pushed may even run under. Lots of flam involves paying a different penalty - the boat stops dead each time she pitches. On the whole, a moderately rounded stem and somewhat cutaway forefoot seems best.

[Kermit]

Check this stem:

http://www.macnaughtongroup.com/puffin.htm

[Ian G Wright]

Originally posted by Kermit:
Check this stem:

http://www.macnaughtongroup.com/puffin.htmOo er! Distorted or what? Looks like a boat from the Robin Williams version of Popeye.

IanW.

[Meerkat]

Pre-WW I warships had bows like that! I vaguely recall reading something dirisive about the 'canoe fleet' :D

Actually, I don't think it looks all that bad.

[ACB]

Those warships had ram bows. An armour-plated projection of the keel, below the waterline, intended as a means of sinking an enemy ship - the idea derived, of course, from the Greek and Roman galleys and their descendants, the galleys of the Mediterranean sea up to say 1820.

Unless I am much mistaken, there was only one sucessful ramming in combat but there was a horribly sucessful one in the British Mediterranean Fleet on the 22nd of June 1893. For some reason, Admiral Tryon, a ferocious disciplinarian, ordered his two columns of ironclads to execute a 180 degree turn towards each other, although they were steaming six cables apart and each ship required eight cables to turn 180 degrees.

The CAMPERDOWN, leading the second division's column, rammed and sank the VICTORIA, Admiral Tryon's flagship, sinking her with the loss of 358 men, including Admiral Tryon. 357 were saved, including Commander John Jellicoe, VICTORIA's Executive Officer, who commanded the Grand Fleet at the Battle of Jutland.

Admiral Tryon's last words were "It was all my fault", which indeed it almost certainly was.

[ 10-11-2002, 09:32 AM: Message edited by: ACB ]

[Bruce Keefauver]

For more information re/ Admiral Tryon's boo-boo I can highly recommend one of the best Naval History books recently published (1996); "The Rules of the Game" by Andrew Gordon.

[John E Hardiman]

Originally posted by ACB:

Unless I am much mistaken, there was only one sucessful ramming in combat....Actually, there have been many successful rammings in combat, mostly in the American Civil War, and a handful of DD/SS encounters in WW1 and WW2. If you mean ram bow ship (as opposed to a ship fitted with a ram) hitting, I can only think of two, HUSCAR(?) in Chile hit somebody after launching a Whitehead torpedo if I recall correctly, and FERDERNAND MAX(?) ramming REAL 'de ITALIA in the war for Italian Independence.

[ACB]

I stand corrected. Yes, I meant ram bowed ships, and it was the Italian/Austrian case that I had in mind. The RN destroyer "Spitfire" rammed a German light cruiser in the night action during the final stages of the Battle of Jutland but she certainly did not have a ram bow.

[Ian G Wright]

At the risk of destroying my only RN fantasy,,,,,, do you mean to tell me that no one ever said " Chief, give her everything you've got. I'm going to ram the H** B******!"
or
"Number one... Battle Ensign if you please."
What else is fiction?
"Damn the torpedoes!" ?
"Nelson confides that every man will do his duty."? (so much better than "England Expects...")

IanW.

[ACB]

"There's something wrong with our d****d ships today!", spoken by Admiral Beattie to his flag captain during the battle of Jutland, as the battle cruisers "Invincible", "Inflexible" and "Queen Mary" blew up, is well attested. "Nelson Confides...." likewise, but the telescope to the blind eye is fiction, it seems.

During WW1 Holland was neutral so the ferries kept on running, across a very unfriendly North Sea. Captain Fryatt of the Great Eastern Railway steamer "Brussels" was twice stopped by German submarines and escaped by attempting to ram the submarine. He was captured and hanged by the Germans because as a civilian he had engaged in warlike activities out of uniform.

[Alan D. Hyde]

In World War II, the U.S.S. Borie rammed and boarded (and was in turn boarded by) a U-Boat which subsequently sunk. The Borie herself was badly damaged.

The remarkable incident (involving hand-to-hand combat using fists, knives, and dinner plates, among other things) is well-told in Samuel Eliot Morison's History of United States Naval Operations in World War II.

Morison's history is an excellent read, and would, I suspect, interest many Forum participants.

Alan