Trident 24 - any good?

[bob26]

Agreed - I certainly never changed the angle of the prop shaft on mine - but the prop change made a big difference. If Castlemarine's theory is right then why?

My experience was also that a prop change made a difference on the same hull and shaft angle.

The Castlemarine explanation does allow that changes in pitch or diameter could also affect things. But I suspect there are more forces at work than the Castlemarine's explanation allows for. A prop does not operate in unconstricted water but is likely to influenced by the hull close above it - often a hull sloping upwards at the aft end. When a boat is travelling forward the prop wash is likely to exit relatively evenly into a greater expanse of water since the hull usually slopes upwards up behind it. In reverse the wash may be into the opposite: a constriction in the flow created by the hull.

If the flow from the top of the prop hits the slope of the hull sooner than that from the bottom of the prop this might well cause asymmetry in its effect. This assymmetry might even be greater with a prop shaft that was horizontal than with an angled shaft. The upper blades of the prop may also suck down air causing them to have less push or grip than those below. In an extreme situation a prop that was not fully submerged would act even more like a paddle.

Perhaps Albin Vega owners (with their celebrated propwalk) would care to comment. Their prop shafts look about as nearly horizontal as its possible to be in a smallish boat to me.

One thing is for sure in my experience. Prop walk can be an advantage as often as a disadvantage.

 

[bob26]

Transatlantic Trident

Hi

I'm thinking about buying a Trident 24 as my first proper boat. To me they look the business, like a boat ought to look. But has anyone got any experience of sailing or owning one? They seem reasonably priced. But what do they sail like? And are there any known weaknesses I should look out for?

Kelvin

I have just read an account by David Rudling who crossed the Atlantic to St Lucia at the end of 1999 in a Trident 24 called Dawn Treader (formerly Quintet).

His route (Southampton, Plymouth, La Coruna, Vigo,Madeira, Las Palmas, Mindelo, St Lucia) amounted to 4,715 miles. He spent 1,129 hours (47 days) at sea and averaged 4.2knots over the whole journey (100 miles a day). During the final stage he overtook a Westerly Centaur which made it to St Lucia two days after Dawn Treader.

He concluded: "Few people would argue that the Trident is the ideal boat for such a voyage....but I never had any doubt in the capacity of the boat to see me safely across the Atlantic."

The only changes he made to the standard Trident were:

- Increased size of forestay and backstay from 5mm to 6mm.
- Strengthened the chain plates
- Fitted a vane steering gear
- sealed the forehatch with a strongback
- mast steps (used mid ocean to replace the main halyard block which came adrift)

 

[bob26]

Ooops - wrong departure date

I have just read an account by David Rudling who crossed the Atlantic to St Lucia at the end of 1999 in a Trident 24 called Dawn Treader (formerly Quintet).

Sorry I made a mistake here - David sailed his Trident across in 1992/93 (I was mislead by the date of publication of the account I read - Check your facts properly Bob26!).

 

[Kittyhawk]

A fantastic achievement for a 24 footer whenever it was. Like I said, Tridents are great little boats.

 

[kelvin]

I have just read an account by David Rudling who crossed the Atlantic to St Lucia at the end of 1999 in a Trident 24 called Dawn Treader (formerly Quintet).

His route (Southampton, Plymouth, La Coruna, Vigo,Madeira, Las Palmas, Mindelo, St Lucia) amounted to 4,715 miles. He spent 1,129 hours (47 days) at sea and averaged 4.2knots over the whole journey (100 miles a day).

That sounds amazing. Where did you read this account? I'd love to read it myself.

Kelvin

 

[bob26]

That sounds amazing. Where did you read this account? I'd love to read it myself.

Kelvin

I read it in an old copy of Trident News - the Trident Owners Association newsletter. I found it very interesting and I'm hoping that it can be put up on the TOA website soon. If it is, I'll PM you Kelvin. If you can't wait for that, PM me and I'll send you a copy.

 

[Ubergeekian]

Theory behind propwalk here: http://www.castlemarine.co.uk/download/propwalk.pdf.

I'm not at all convinced by that explanation. Three problems:

1. It predicts that propwalk gets larger as the boat speeds up, with none at all when the boat is stationary.
2. It depends on a thrust differential from one side of the propeller to the other - that's typically 12" or so. Not much yawing torque.
3. It predicts exactly the same strength of propwalk in forward and reverse

And, just to round things off, my nice new boat has (a) a near-as-dammit horizontal prop shaft and (b) lots of propwalk.
I think it's a free surface effect: the top blade of the prop does less because it can more easily create vertical disturbance than the bottom one.

 

[oldharry]

Well, thats why I put it up - the theory sounds fine, but just didnt seem to fit the facts!

Maybe the other theory is nearer the mark after all (and I still cannot find the source): that the greater water density at the 'deep' end of a prop is enough to cause the paddlewheel effect on a slow moving prop

That seems to be nearer what actually happens - but I still am not convinced a foot depth would make that much difference in water density?

 

[Ubergeekian]

That seems to be nearer what actually happens - but I still do not convinced a foot depth would make that much difference in water density?

It wouldn't. The pressure difference is density x depth x g so at 30cm that's 1000 x 0.3 x 9.81 = 2943 Pa. The coefficient of compressibility (bulk modulus) for sea water is 2.3 GPa. That gives a decrease in volume, and therefore an increase in density, of 0.000128%

I'm sure it's a free surface effect. Stick an oar blade just below the surface and pull hard. Big wave, easy to pull. Stick it well underneath and try again. Much smaller wave, much more resistance.

 

[bob26]

Surface effect...?

I'm not at all convinced by that explanation. Three problems:

1. 
   ...the top blade of the prop does less because it can more easily create vertical disturbance than the bottom one.

1. 
   
   Even if there is a solid hull above it rather than air?

 

[Ubergeekian]

Even if there is a solid hull above it rather than air?

Good point. Dunno. I would expect any effect - well, not this one - from a prop close under a very broad, flat hull. Anyone got such a thing?

 

[bob26]

Good point. Dunno. I would expect any effect - well, not this one - from a prop close under a very broad, flat hull. Anyone got such a thing?

If you Google "prop walk" you get as many explanations as you like.

“Propeller walk is a complicated effect which depends on ship geometry, direction of travel, propeller direction, vessel speed and depth of water,” according to:

http://en.wikipedia.org/wiki/Propeller_walk

“Prop Walk is not caused directly by a side thrust from the propeller but by the wash off the propeller blowing back over the hull and in effect creating a lifting effect to one side from the asymmetric flow from the propeller over the hull.”

www.kiwiprops.co.nz/prop_walk.html

This bloke supports your surface effect explanation (I think) “…any tendency for the prop to discharge water radially at the bottom of its arc will involve driving that water into other (incompressible) water, whereas at the top of the arc, water thrown out radially can move into air. Thus, there will be more lateral slip at the top than the bottom, again causing "walking".” But then he goes on to cite three other possible causes.

http://www.irbs.com/lists/navigation/0304/0157.html

And so on...

 

[Ubergeekian]

If you Google "prop walk" you get as many explanations as you like.

Thanks for going to all that trouble. Sounds like a good PhD for someone keen.

 

[Kittyhawk]

Article on the Trident 24

Hi

I'm thinking about buying a Trident 24 as my first proper boat. To me they look the business, like a boat ought to look. But has anyone got any experience of sailing or owning one? They seem reasonably priced. But what do they sail like? And are there any known weaknesses I should look out for?

Kelvin

I see there is an article on the Trident 24 in the latest Sailing Today.

 

[Kelpie]

I see there is an article on the Trident 24 in the latest Sailing Today.

Either I've gone blind or my copy is missing that article...

 

[kelvin]

What month are you talking about?

Sailing mags always seem to be GMT + 1 month.

 

[bob26]

What month are you talking about?

Sailing mags always seem to be GMT + 1 month.

Quite right Kelvin. Instead of Sailing Today perhaps it ought to be called "Sailing The Day After Tomorrow".

There is a one-page article on the Trident by the acting editor Rodger Witt on page 78 of the February 2010 issue. Calls the Trident "something of a classic" and "a thoroughly sensible little boat". I won't argue with that.

 

[Kelpie]

Ah that explains it. I got a ST sub as a Xmas present and the first issue to arrive was March, so I'm now reading the April one. I have a hard enough time keeping track of time as it is without this sort of thing happening...

 

[Kittyhawk]

Ah that explains it. I got a ST sub as a Xmas present and the first issue to arrive was March, so I'm now reading the April one. I have a hard enough time keeping track of time as it is without this sort of thing happening...

Sorry Rob. Should have made it clear what issue I meant...its still only Feb down here. You haven't missed a huge deal. The article isn't very informative.

 

[kelvin]

You haven't missed a huge deal. The article isn't very informative.

I agree with you Kittyhawk. I borrowed a mate's copy after reading about the article here. I think I learned more about the Trident from this forum than I did from the ST article on the Trident. Even the pictures were better on here. I don't know how they can expect you to pay for such thin stuff when you can get so much first hand experience and help here.The Trident owners website has a lot of useful free information on it too.

Kelvin