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marujo.sortudo · 12-12-2009, 12:57

The Tahiti ketch is a famous John Hanna design which had been influenced by some Colin Archer designs which in turn where based on some of the old North Sea folkboats. Atkin has some lovely designs, too, but the Tahiti ketch isn't one of them.

**James S** · 13-12-2009, 08:27

Thanks for clearing that up guys.

Blue Stocking · 13-12-2009, 10:04

Zeyang,

Have you done calculations on factors such as ballast ratio, and CE/CLR at heel angles, that you would be prepared to share with us.
The reason I ask is general interest about double-ended designs.
Having sailed both Tahita ketch, which has a fine underwater entry and exit, which is carried on above the waterline, and short overhangs, IMHO, made the boat "hobbyhorse" in short steep seas. The snug gaff rig, of 450 sq ft. didn't have much drive to windward, but was great from about 60* to dead aft.
The Venus boats (more like Colin Archer) had a less fine entry and fuller exit, which was carried above the waterline, more so at the stern, and therefore, IMHO, were more stable in their forward motion in short seas.
What material masts will you use.
The heavier wooden spars of these original boats helped smooth the athwartships roll.
This same comment has been made by some Rhodes Reliant owners ( of which I am one) who changed the wooden spars to aluminum, (not me) only to find that the lighter spars made the boat "stand up" more, and not get her shoulder down to the optimum sailing angle.
Curious as to what the forum thoughts are.

zeyang · 13-12-2009, 12:10

Quote:

Originally Posted by Blue Stocking

Zeyang,

Have you done calculations on factors such as ballast ratio, and CE/CLR at heel angles, that you would be prepared to share with us.
The reason I ask is general interest about double-ended designs.
Having sailed both Tahita ketch, which has a fine underwater entry and exit, which is carried on above the waterline, and short overhangs, IMHO, made the boat "hobbyhorse" in short steep seas. The snug gaff rig, of 450 sq ft. didn't have much drive to windward, but was great from about 60* to dead aft.
The Venus boats (more like Colin Archer) had a less fine entry and fuller exit, which was carried above the waterline, more so at the stern, and therefore, IMHO, were more stable in their forward motion in short seas.
What material masts will you use.
The heavier wooden spars of these original boats helped smooth the athwartships roll.
This same comment has been made by some Rhodes Reliant owners ( of which I am one) who changed the wooden spars to aluminum, (not me) only to find that the lighter spars made the boat "stand up" more, and not get her shoulder down to the optimum sailing angle.
Curious as to what the forum thoughts are.

Hi, I havent started doing any calculation regarding the sailplan yet. I will make a model and start to fiddling with this, hopefully in february.
the ballast will be in ingots so it will be easy to move back and forth.
I have read about others who have found swapping from wood to alloy mast have made a significant difference feeling of sailing a colin archer. What I can do to compensate this is to stuff lead into the top of the alloy mast :-) or ofcourse choose a pine-mast, but since boat is in alloy it will make it easier for me to choose alloy-tube as a mast. Another thing i would like to have is a deck stepped mast to make it easier to move it back and forth on deck and also lower it.
(reweld the tabernackle in a new position if i need)

zeyang

zeyang · 13-12-2009, 13:53

Quote:

Originally Posted by marujo.sortudo

The Tahiti ketch is a famous John Hanna design which had been influenced by some Colin Archer designs which in turn where based on some of the old North Sea folkboats. Atkin has some lovely designs, too, but the Tahiti ketch isn't one of them.

this is an interesting observation. Mr Archer observed the old pilot boats (Hvaler skiffs) which has a very low freeboard but overall looks like a double-ender. And probably the designer of these pilot boats got their ideas from even older boats all the way back to the viking boats which u can observe today (see the oseberg viking boat) which is also a kind of a double ender with very low freeboard but a little stretched out.
So the traditon goes back at least 1000 years more or less.
both the vikingship and also the whaler ship was clinker built and also the first Mr Archer designed was clinkerbuild until he switched to carvel. but i must say i think clinker is estetically more pleasing to eyes.

zeyang

marujo.sortudo · 13-12-2009, 17:14

Ah, thanks for catching me, I should have said "pilot boats" not "folkboats" ... ooops

. I do love clinker/lapstrake construction, too.

There's a lovely article in the January 1913 issue of Rudder (reprinted in The Rudder Treasury edited by Tom Davin) about the analysis of the Viking ship unearthed at Gogstad in 1880. Here's a tiny taste:

"...It is the opinion of the experts in naval architecture that for model and workmanship this vessel is a masterpiece, nor for beauty of lines and symmetrical proportions could she be surpassed today by any man connected with the art of designing or building ships. Certainly a strong statement, in view of the fact that we have a thousands years' more experience, but nevertheless true. It is doubtful if there are in this country today a score of men with enough innate ability to design a boat, for the purpose intended, equal to this one in appearance, seaworthiness and speed. With regards the two latter qualities, she is worthy of careful study.

The lines of the ship were taken off by Mr. Colin Archer, and along with other data embodied in a paper read before the Institute of Naval Architecture in 1881. ...."

MichaelC · 13-12-2009, 17:31

Ahh, NotSure. I had an aluminum schooner for ten years. Aluminum frames and longitudinals. Fantastic boat. When I sold her there was no, repeat NO pitting or electrolysis or any other kind of problem. Use aluminum with aluminum. I had galvanized grease fitting below the waterline which gave no problems. No stainless. Bad idea. If I could afford to build my new boat in aluminum I would not hesitate. But it has to be in marine plywood. In terms of strength, I once hit a log raft under full sail with lots of wind in the middle of the night. I once slammed into a fuel dock. I once clipped a coral reef. [Well I was learning, okay?...] She was sleek, powerful and a tank. Aluminum is the boss, dude.

johnar · 13-12-2009, 17:34

Lap = alot of welds, welds = heat. aluminum dose not like heat at all. I do not understand why sheet was not used.

Dutch

MichaelC · 13-12-2009, 17:36

As to Viking design, I built two faerings [hardangers, whatever] based on the lines from the faering found with the Gokstad ship. I was absolutely astonished by the speed, tracking ability and seaworthiness of this thousand year old design. Those Vikings really knew what they were doing. And the Norweges are still building to the same design. For good reason ....

zeyang · 13-12-2009, 23:14

Quote:

Originally Posted by johnar

Lap = alot of welds, welds = heat. aluminum dose not like heat at all. I do not understand why sheet was not used.

Dutch

when we talk about 8 mm alloy with overlap (means 1.6 cm) the spread of heat is tremendous. Besides i will switch to MIG which is a faster way of welding to minimize the risk of heat buildup.

zeyang

zeyang · 13-12-2009, 23:21

Quote:

Originally Posted by MichaelC

As to Viking design, I built two faerings [hardangers, whatever] based on the lines from the faering found with the Gokstad ship. I was absolutely astonished by the speed, tracking ability and seaworthiness of this thousand year old design. Those Vikings really knew what they were doing. And the Norweges are still building to the same design. For good reason ....

Good seaboats for sure. Here is one in production. this is classical style. Im not even close to build something like this.
Working with wood is very different since its a live material. I use sledgehammer, grinder and weldingmachine to force things into position. :-) They use steam and love! :-)

zeyang · 13-12-2009, 23:25

Quote:

Originally Posted by MichaelC

As to Viking design, I built two faerings [hardangers, whatever] based on the lines from the faering found with the Gokstad ship. I was absolutely astonished by the speed, tracking ability and seaworthiness of this thousand year old design. Those Vikings really knew what they were doing. And the Norweges are still building to the same design. For good reason ....

Here is picture of that Gokstad ship. There is not much difference between this 1000 year old boat and the other small one they guys are building.
You see space for the oars there. What i didnt grasp: they never seem to think about some deck to make the plunderingjourneys a little more pleasant.
The cold north-sea dripping down they neck cant be that cool. but hey, they were vikings! :-)

zeyang

zeyang · 13-12-2009, 23:28

Quote:

Originally Posted by zeyang

Here is picture of that Gostad ship. There is not much difference between this 1000 year old boat and the other small one they guys are building.

Actually i was studying this ship closely when i was making planks for my project. So I end up with same amounts of planks. This one is a little more narrow in the bow due to different bowshape, and since they use wood they need to take this into account when fastening up. (wood/iron plugs i think)

Alloy and weldingmachines was not invented yet. :-)

zeyang

anjou · 13-12-2009, 23:47

As well as travelling vast open sea distances, the Vikings also explored a lot of rivers far inland, like the Volga in Russia all the way to the Black Sea, so a light boat was very important to be able to Portage over rapids and shallows.
Maybe this is why the boat is a stripped down vessel with no floor which also makes bailing out easier.

The time and materials needed to make a wood boat is huge so maybe leaving out the home comforts helped with costs. Quite by chance, I saw a National Geographic prog on TV while I was on the ferry this week on the way back to UK showing a Longboat replica being built.