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S&S Swan Maintenance - Prism dimensions (411)
06 June 2014 - 13:13
#1
Join Date: 12 February 2014
Posts: 23

Prism dimensions (411)

I want to replace the prisms (they're old, and not in great condition) on Sophie B, but I'd like to get the new ones made before attempting to remove the current ones - time for manufacture; and the fact that the current ones have been repeatedly unsuccessfully sealed to tame a leak, so removing them will be a mission; and that it's winter here all pointing to this decision.

I have found a plexiglass manufacturer who is able to mould the pieces, but need the exact dimensions.

Anyone?

Tom

11 June 2014 - 18:57
#2
Join Date: 16 May 2009
Posts: 252

I want to replace the prisms (they're old, and not in great condition) on Sophie B, but I'd like to get the new ones made before attempting to remove the current ones - time for manufacture; and the fact that the current ones have been repeatedly unsuccessfully sealed to tame a leak, so removing them will be a mission; and that it's winter here all pointing to this decision. I have found a plexiglass manufacturer who is able to mould the pieces, but need the exact dimensions. Anyone? Tom

Tom:

The previouis owner of my 411 replaced the prisms - I'll check with him to see if he was able to buy them as finsihed parts, or how he went about it.  I will let you know what comes back.

All the best - I hope everyone has a nice weekend sailing...

Geoff, Corazon, 411 #41

12 June 2014 - 09:04
#3
Join Date: 12 February 2014
Posts: 23

Tom:

The previouis owner of my 411 replaced the prisms - I'll check with him to see if he was able to buy them as finsihed parts, or how he went about it.  I will let you know what comes back.

All the best - I hope everyone has a nice weekend sailing...

Geoff, Corazon, 411 #41

Dear Geoff


Thank you very much! Would be most grateful if you have any information.


Have entered one of the inner circles of hell with Nautor over this. I wrote last week to their spare parts division, asking for dimensions and/or drawings, to which they responded that they could not provide the drawings. I then asked if they had spare prisms themselves, to which they replied no, but gave me a link to a company in Germany that makes glass prisms (http://www.toplicht.de/en/shop/fenster-bullauge-luke-und-luefter/deckslicht-und-rahmen/decksprisma-glas-davey-fuer-rechteck-ring ). (But I thought the originals were plexiglass?)


And it is not clear whether any of the three prisms on the page linked are the correct dimensions.... So I have asked them again, if they could just provide the measurements ....


To compound my problems, the prisms I have are the originals (35 years old!) and have been heavily Sikaflex'd in - in part because one of them is cracked and leaks... So I am loth to remove them until I have new ones to slot in ...


Speaking of which - anyone with ideas as to how to best remove the Sikaflex? Cut it away with a sharp knife/chisel?


Cheers!

12 June 2014 - 12:50
#4
Join Date: 06 February 2007
Posts: 49

Tom, the Hamburg based company "Toplicht" has got a good reputation with classical boats. As I am living in Hamburg... in case I could be of any help just let me know.

Toni

(toge, 38/113)

 

13 June 2014 - 02:09
#5
Join Date: 20 March 2011
Posts: 88


Tom

I replaced the prisms on 44-004 Hatha,don't know if they are the same size as yours

They are made of acrylic by a company in Massachusetts that specializes in making custom hatches, etc. I sent them a dimensioned drawing and they made them on a cnc router out of 1 solid piece of acrylic, so no glue joint between the mounting flange and the prism.

They are beautifully done and the cost was around $300 U.S. I will find the info for you tomorrow and post it

Tonyh 44-004 Hatha

13 June 2014 - 07:55
#6
Join Date: 12 February 2014
Posts: 23

Tony
Thank you very much

That would be brilliant.

Kind regards
Tom
(Sophie B - 411/025)

13 June 2014 - 18:22
#7
Join Date: 20 March 2011
Posts: 88


Tom

I just spoke to Tony who made my prisms- email tony@selectplastics.com, and he is going to look for my file.

Meanwhile, here's what I sent him to work from

I used my teak deck caulking to bed the prisms- Teak Decking Systems SIS 440. It's a silicone compound, plastics don't like polysulfide caulks.

Best of luck,

Tony

13 June 2014 - 19:50
#8
Join Date: 12 February 2014
Posts: 23

Thank you! Will check if it's the same as the 411s. I can't imagine that they would have different specs. But nothing would surprise me now!

Happy weekend and happy sailing!

23 June 2014 - 23:36
#9
Join Date: 12 February 2014
Posts: 23

OK - After much measuring, and with great assistance from Tony (see earlier posts) - I think the attached is a pretty good replica of the original decklight prisms.

The only material change is the raised portion at the top, to better fit the stainless steel cover plate, and with adequate room then to seal between the cover plate and the plexiglass. It will also allow the frame and the plexiglass to be on the same plane. This seems a good idea. Is it?

Will get two made up for Sophie B in plexiglass as a single element (rather than the three components). If the manufacturer I found in Johannesburg can do it, and they are reasonably priced, I shall report back.

Thanks for all your help and advice!

Tom
(411/025 - Sophie B)

24 June 2014 - 13:16
#10
Join Date: 30 January 2007
Posts: 444

Tom and Tony,
just a comment looking at your designs - assuming that I interpret them correctly, not at all a certainty, of course. A thickness of 6mm or 6.3mm of the side support seems a bit small to hold the unlikely but possible point weight of an unaware passenger. Are you positive that the original is like this?
Daniel, 411/004

24 June 2014 - 17:15
#11
Join Date: 20 March 2011
Posts: 88


Dear Tom and Daniel

The dimensioning I provided was taken from the prisms I removed from the boat which was 12 years old when I bought her, so I assume they were original.

Intuitively speaking, I think the very short unsupported span is plenty strong, supported on all 4 sides by the 6mm flange. It seems the prism itself would add support lengthwise as well. I'm sure the Professor could calculate exactly how much point load the assembly could carry.

Brilliant idea for the raised portion in the center, I wish I had thought of that myself. I will resist the temptation to re-do my own.

One thing I did do was to have new stainless flanges made for the prisms and recessed them flush into the new teak decks, as I did with all of the surface mounted hardware- pad eyes, stanchion bases, chainplate escutcheons, etc.

Happy sailing

Tonyh

24 June 2014 - 17:33
#12
Join Date: 12 February 2014
Posts: 23

Thanks Tony and Daniel

I was concerned by that, too, initially, but the thickness of the exposed plexiglass will be 11mm, with the thinner portion covered by the stainless steel cover plate. And the 5mm raise will allow c. 3mm sealing between the plexiglass and the steel. Is that perhaps too much? No matter, I want these to be absolutely watertight!

Tony, I like the idea of making the whole lot flush with the deck, rather than 1-2mm above... But that would mean redecking. Not going to happen soon, sadly!

I am speaking to a moulder here who says it will not be a problem to mould this as a single unit with no bonding between layers. If I get anything sensible, I will post pictures for anyone else who is thinking of going this route. If I'm happy with the result, also happy to help others (e.g. by posting!).

Tom
(411/025 - Sophie B)

24 June 2014 - 21:06
#13
Join Date: 02 January 2008
Posts: 1535

Dear Tom and Tony
The strength of the prism as shown appears to be sufficient. A rough calculation suggests that if a heavy person steps onto the prism with one foot this leaves a safety factor of about five in both bending and shear along the edges.
Tools dropped from the rig is a different matter, this may shatter the material.
The sealant thickness should be related to the heat expansion difference between the stainless frame and the acrylic prism. Do you know if the plexi material is cast or extruded? The latter has an expansion coefficient about three times bigger.
Would suggest that 3 mm sealant thickness is marginal.
Consult Sika Marine Application Guide for advice referring to sealant type and thickness.
Kind regards
Lars

24 June 2014 - 22:11
#14
Join Date: 12 February 2014
Posts: 23

Lars

Thank you for your wisdom. I will certainly check with the manufacturer if it is to be extruded or not....

This has also alerted me to the fact that the interior dimensions of the steel frame are 320 x 50 ... so designing for an exact fit is probably not sensible at all, although it seldom gets below 8 degrees celsius here.

Perhaps it's also a good idea to increase the height of the lip - it was a stab in the dark as a first guess (based on 1-2 mm for the stainless steel cover, and the rest for sealant.

Now to read up on relative expansion factors of polished SS vs. plexiglass!

I sense v2 of the design coming along soon ...

Tom

PS: Lars, I have seen your previous post about Sikaflex and acrylics. Others on the forum talk of using the teak caulking as a sealant. Which would you recommend?

25 June 2014 - 13:57
#15
Join Date: 02 January 2008
Posts: 1535

Tom
The chemical resistance of acrylic is not very good, and the solvents contained in some mastics may cause crazing. In chemical terms acrylic is not resistant to organic compounds, chlorinated hydrocarbons, ketones and esters.
It would be advisable either to find out the exact composition of the mastic of interest, or stay with products promoted by the manufacturers for this use.
Kind regards
Lars

05 March 2017 - 10:13
#16
Join Date: 27 January 2011
Posts: 130

I have now had our two pisms custom made at EUR 125 (tax incl) a piece in Germany; I do not have any price comparison, so I cannot tell if this is cheap or expensive. The quality is excellent. It will very much improve the light situation in the head, given the old ones were very dull.

They were made waterproof with a layer of rubber between the plexi and the aluminum cover. This layer needs to be replaced too.

 

Christian IF 411/028

06 March 2017 - 08:23
#17
Join Date: 29 January 2007
Posts: 888

Dear Friends,

I just ordered two prisms for Vanessa and I paid Euro 120 plus VAT, so I think this is an average price!

Fair winds

matteo (47/069 Vanessa)

09 March 2017 - 12:52
#18
Join Date: 01 September 2007
Posts: 15

Dear Matteo,

Dear Christian,

May I ask your for the adress of the company producing your prisms?

 

Thank´s very much

Best regards

Klaus, CARISSIMA, SWAN-38

09 March 2017 - 19:23
#19
Join Date: 27 January 2011
Posts: 130

Hi Klaus, in my case this was marinacryl.de .

 

Regards,

Christian

10 March 2017 - 08:05
#20
Join Date: 29 January 2007
Posts: 888

Dear Klaus,

in my case Plexidea from Viareggio (Italy)

Fair winds

matteo (47/069 Vanessa)

05 June 2017 - 17:40
#21
Join Date: 27 January 2011
Posts: 130

 

I finally found time to install the prisms. The photo will help you assess what needs to be done if you change them. I used butyl tape to make the prism itself watertight in its seat. I then placed a new sheet of rubber 2mm on top of the prism, cut to fit the aluminum cover. I then screwed the cover back on, making the screw holes watertight with butyl wrapped around the screws. I finally added a new seam of Sika around the outer edge of the aluminum plate.

The light situation below deck is very much improved. Funny enough, the new prisms project nice rainbow patterns to the floorboard when the sun is shining.

 

Christian IF 411/028

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