Vintage Gentleman’s Cruiser

[lnvisiblemanParticipant @lnvisibleman]

Gareth   cc Dave,  Paul

a wonderful technical response that all falls apart because of the first statement , "If you assume"

Most assumptions are simply opinion so that is not a good basis to argue from. However, it does remain a fact that, with any marine or aviation propeller, not all the thrust is parallel to the shaft line. There is also an amount of thrust in an outward direction ( centrifugal force ) that is not taken into account in your calculations. Neither is the rotational force induced in water or air by a spinning propeller.

I am not saying that your conclusion is either correct or incorrect, just that it has been reached with less than perfect mathematical methodology

To be convincing in any way, I would suggest that you demonstrate a far more accurate and realistic model of performance given by a propeller. It would only be correct for a stated size and pitch, but would be a starting point for sensible discussion. That would seem a better course of action than just putting down ideas for the simple reason that there is disagreement

Let's see some proof either way.

Ref Fairey pics, the shafts are at that angle because " They couldn't fit then in any other way ! Unless there is documentation to the contrary ??

Mike ( I can take any amount of sniping from those nasty men !

Edited By lnvisibleman on 18/09/2014 00:28:21

Edited By lnvisibleman on 18/09/2014 00:30:05

Edited By lnvisibleman on 18/09/2014 00:31:58

[ashley needhamParticipant @ashleyneedham69188]

The only way to sort this is to build two identical boats, one having a very shallow prop angle and one having a steeper (or steep, for the sake of experimantation) and then power them identically and see what the difference is side by side.

HOWEVER a downwards pointing shaft does not look right at all, and I think that the designer should go a certain, if not LONG length to make the shaft angle shallow. I would have thought that the actual difference is in the long term…fuel consumption vs speed and so on, for a full size boat.

(usual disclaimer applies)

Ashley.

NB no actual scientific fact was applied to this post

[Bob Abell 2Participant @bobabell2]

While you lot argue the toss about the Angle of Dangle of the prop shaft, the rest of us can take a look at the latest work in progress

Made a start on the cabin construction

It will be great fun laying out the rooms and stuff

Bob

[Paul TParticipant @pault84577]

Dear All

I would suggest that those doubting the science take a couple of years off to research relativistic physics, the short version which specifically deals in fluid dynamics, this entry level research will level out the playing field and result in enlightenment we could then resume the conversation from a point of equal understanding.

Meanwhile I will muse over my muse and come up with something comical or amusing.

Paul

Edited By Paul T on 18/09/2014 13:07:07

[Paul TParticipant @pault84577]

To pre-empt any further half baked theories I should point out that there is no such thing as centrifugal force, the term centrifugal force is a misnomer as the apparent effect actually applies to inertia of motion.

The motion relating to rotation is called centripetal force (Fc = mv2/r) and was first described by Newton in 1684.

Dave is right about my muse but rather than fettering it I see the process as the purity of design and the need not to compromise, I agree that this pursuit of purity can raise more problems such as whipping of unsupported shafts in long prop tubes however the same pursuit of purity provides the answer to every problem which in this case is the addition of additional bearings within the tube.

Yes long prop shafts with internal bearings are expensive but you can always build your own as parts are readily available.

Paul

 

 

 

Edited By Paul T on 18/09/2014 15:39:03

[ashley needhamParticipant @ashleyneedham69188]

Bob. I dont think we are arguing about the angle of the dangle, we are giving input, as the angle of the shaft has been a constant theme in Pauls designs.

The designer has the last say. he is the designer and he has the computer programs to back this up, and this is exactly as it should be. IF I were making a Paul design, i would build as-is.

Ashley

[Dave MilbournParticipant @davemilbourn48782]

Nicely put, Ashley. I don't agree that steep shaft angles necessarily reduce performance by an unacceptable degree but I did build Paul's Sea Spray design as per plan. That said, the angle of dangle on my new model is like a ruddy escalator…….but it's a scale model so, as Ash says, that's exactly the way it should be. Not that Mr T would pay a blind bit of notice to what I think anyway!

DM

[Peter FitnessParticipant @peterfitness34857]

That's looking good Bob, but I wish Paul would stop using such big words, I'm wearing my dictionary out looking up all the meanings

[CookieOldParticipant @cookieold]

Hi All , It would be very simple to overcome the long shafts whipping by just removing the bush from one end , then get a parallel bush with a groove around the OD ( outside diameter) to retain the adhesive make it a slide fit in the tube applie bearing fit Loctite and slide the bush down the tube to the center and let set then replace the end bush job done.

Dave

[Bob Abell 2Participant @bobabell2]

Good idea, Cookie

As another idea, we could use two complete propshaft tubes per shaft?

Or two complete propshafts with a coupling in the middle?

Bob

[Bob Abell 2Participant @bobabell2]

Work in progress

Made another small mod

Moved the cabin forward by 180mm in keeping with the photographs

Hope it meets with Drawing Office approval?

Having great fun working on this model, but deep down, I'm beginning to think, it's a bit impractical?

The crunch will come when it's time to purchase the gear!

Bob

[Mark Jarvis 2Participant @markjarvis2]

HI Bob

Don't forget its the club bring and buy in 2 weeks, could be all you need is on the tables????

Mark

[Bob Abell 2Participant @bobabell2]

Thank you, Mark

I doubt it really, but worth a look

Bob

[Paul TParticipant @pault84577]

Bob

Its looking great but I think that my original design for the forward windows is wrong for your version and that the openings might look better at the same size as those on the sides.

Why impractical? Its only 5ft long and it will give you the chance to demonstrate your fitting out skills with polished brass and etched glass.

Paul

[Bob Abell 2Participant @bobabell2]

Thank you, Paul

I agree, the cabin is looking out of proportion now

Will look into why the change has come about and put it right, it's only wood

Going off memory, the only changes are…….Transom has sloping sides……decks raised to bulwark height and cabin moved forward

Bob

[Paul TParticipant @pault84577]

Bob

To explain the content of your last post we should tell the readers that we have had a private conversation about the build.

Re the proportions: The apparent increased height of the superstructure is due to raising the decks and getting rid of the bulwarks both of these actions have had a compound effect on the proportions.

Paul

[Bob Abell 2Participant @bobabell2]

New slimmed down version

How`s this Paul?

Bob

[Paul TParticipant @pault84577]

That looks a lot better.

Have you given any more thought to splitting the hull for ease of transport?

[Bob Abell 2Participant @bobabell2]

Hello Paul

Are we having the foredeck cabin overlap or as your original design?

Don`t fancy a split hull at the moment

Might semi finish the build and tow it round the lake at Etherow and then decide about splitting

I will position the motors with the split in mind

Prudence is my middle name

Bob

[Paul TParticipant @pault84577]

Hello Prudence

The long foredeck make the boat look sleek and more graceful but that's only my opinion and you must do what you think best.

I would strongly advise that you split the hull for handling and ease of transport, a split hull will also allow you increase the strength of the boat amidships (this will also help with our little towing contest)

Paul

[Bob Abell 2Participant @bobabell2]

At least, I've got a good reason for building a big model now!

The full size craft has a very nice rear windscreen and seating well, but is not really suitable with the original design

Decisions, decisions

Bob

[Paul TParticipant @pault84577]

Captain Bob

I have been looking at the Vintage Cruiser design with a view to strengthening the hull for towing.

It can be achieved by doubling the thickness of the frames from F4 to F9 and fill the spaces between the stiffened frames with 25 x 30mm timbers, this will make the side decks into a rigid plate that will transfer the towing load around the entire hull, as shown in red below.

The rear deck between F9 and the Transom would also have a strengthening timber of 25 x 400mm running across the width of the hull

The towing point would be at F9

Paul

[Bob Abell 2Participant @bobabell2]

Many thanks, Captain Paul……….We've been away again in the campervan again…..while the weather holds

I have an engineering solution to the so called lack of strength problem

If the motors and prop shafts and the Samson post were bolted to a simple central plank …..That is the simple solution……No strengthening required!……….Unless I've overlooked something?

Also…….If the boat was made of chewing gum and sealing wax……You still wouldn't pull the back off, because I haven't switched the motors on yet!……….Ha! Ha!

As Gareth pointed out, it would cost a small fortune, trying to match the awesome power of Thor, So i shall offer a token gesture only….Four humble MFA 850 motors and see what happens?

Captain Bob

[Paul TParticipant @pault84577]

Hi Bob

Hopefully you and Joyce are having a nice time and not getting to cold at night in the campervan.

Despite your optimistic view I can assure you that there is a very real lack of strength in the Vintage Cruiser design, the 5ft hull is a compromise between size, weight & strength and is designed to simply support its own weight and resist hogging. The oversized stringers have been added into the design to enable the power & torque from the four motors to be equally spread throughout the entire hull.

I'm sorry to say that you have overlooked something and that your plank proposal is doubtful due to the way torque load is exerted on the samson post and could only work if the plank is 1in thick and covers the entire area of the hull base from F3 to Transom.

We cant do a token gesture as so many people are now looking forward to the match, with very little work the Lady Joyce could be turned into a very competitive challenger to Thor, don't forget that those 4 850s geared down and driving some big 4 blade props will be a fearsome combination.

Paul

[Bob Abell 2Participant @bobabell2]

David to Goliath

It's a long time from now to the next show

I'm building a graceful Gentleman's cruiser at the moment, to glide round Etherow Lake at next years regatta's

The funny stuff can come later!

If I select the Samson post position with care, there's no need to beef the frame up anyway!

The Samson post may be under water?

Capt Bob

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