What is the 'correct' name ....

[sundown]

I would appreciate a kick start. I am having a 'seniors moment' trying to identify the correct name for the prism that one can mount in the deckhead to allow natural light into the hull. I want to do an online search to get a feeling for the price of the things so I can put it on my 'Birthday List". If they are really expensive I need to have time to do lots of begging and whining.

[Geno53]

I think you have it right they are called deck prisms.

[Pblais]

"Deck Prism" would be correct. Nothing nautical about the term.

[sundown]

Heck that was too easy ... ! I was sure that I had typed that into the Google search bar with no results but I just checked again and you are right.
Thanks

[Pblais]

We can do "easy".

Not every question posted here has to be hard. Actually it would be nice if folks could post a few easy ones once in a while.

[Sailormann]

The nautical name for it is "deadlight"

[delmarrey]

Then there are fiberoptics..........................._/)

[Terra Nova]

Originally Posted by Sailormann

The nautical name for it is "deadlight"

Yo Sail,

"deadlight" is normally used to refer to any fixed (non-opening) boat window. Deck prism is correct I believe.

best, andy

[Geoff S.]

Terminology aside, they're not terribly expensive compared to many "marine" things. I've seen them range in price from less than 20 bucks for small ones to nearly 200 for big ones that include deck frames. Here are a few sites to look at:
Defender has some small ones, intended as paperweights:
Discount Marine and Boat Supplies - Inflatable Sales - Defender, search keywords "deck prism";
And here are some larger, more expensive ones:
Marine Skylights Boat Deck Prisms
SailBoatStuff Fixed Porthole and Deck Prism
Also, check Sailorman http://www.sailorman.com; they often have a bunch of surplus ones on the shelf for pretty cheap.

Here's a nice 4 1/2 incher you can probably scoop for 5 bucks on ebay:
eBay: Large Ship Boat Deck Prism Mystc Seaport NEW IN BOX! (item 270118694639 end time May-13-07 16:00:28 PDT)

I'm thinking of putting few in my boat too (I may regret handing off that ebay listing!). They do shed a lot of light, and look very salty. My main caveat is to research proper bedding; you are after all drilling a pretty big hole in your deck!

Hope this reduces the Begging and Whining Factor...

[cooper]

Which way up do they go ?......l would neither want to head but it ...or sit on it.....

[Lodesman]

A "portlight" is a fixed non-opening window; a "deadlight" is a cover for the portlight.

Kevin

[TaoJones]

Have a look at this website, sundown.

SailBoatStuff Fixed Porthole and Deck Prism

As far as definitions go, you will find that the terms "port light" and "deadlight" are applied variously and contradictorily, and the original meanings are lost in the mists of time. For me, a port light is the metal and glass structure placed into a port hole, and that can be opened to admit air, while a dead light is a similar metal and glass structure placed into a port hole, the difference being that it is fixed and cannot be opened.

Some apply the term dead light to what I have always called a "deck prism," and I suppose technically it could be used for any non-opening, light-admitting structure place in a deck opening, but it is the prism that differentiates it. The prism helps scatter the light as well as make it less like a window - thus, allowing more privacy.

TaoJones

[Terra Nova]

Originally Posted by Geoff S.

Terminology aside, they're not terribly expensive compared to many "marine" things. I've seen them range in price from less than 20 bucks for small ones to nearly 200 for big ones that include deck frames. Here are a few sites to look at:
Defender has some small ones, intended as paperweights:
Discount Marine and Boat Supplies - Inflatable Sales - Defender, search keywords "deck prism";
And here are some larger, more expensive ones:
Marine Skylights Boat Deck Prisms
SailBoatStuff Fixed Porthole and Deck Prism
Also, check Sailorman http://www.sailorman.com; they often have a bunch of surplus ones on the shelf for pretty cheap.

Here's a nice 4 1/2 incher you can probably scoop for 5 bucks on ebay:
eBay: Large Ship Boat Deck Prism Mystc Seaport NEW IN BOX! (item 270118694639 end time May-13-07 16:00:28 PDT)

I'm thinking of putting few in my boat too (I may regret handing off that ebay listing!). They do shed a lot of light, and look very salty. My main caveat is to research proper bedding; you are after all drilling a pretty big hole in your deck!

Hope this reduces the Begging and Whining Factor...

Yo Geoff,

when installing bonded-in-place fixed windows, I have found that a silicone-based Dow-Corning product #791 (or 795) helpful, in that it allows a huge degree of expansion and contraction without becoming disbonded. I have also used a similar product successfully on deck prism installations. Clean everything with industrial alcohol prior to applying the sealant. It helps to have each piece carefully masked off before installing, and to remove the masking before cure.

I have always found it necessary to custom-fabricate a stainless steel inner and outer frame when installing these prisms, even for those which come with their own thin outer frame.

It is astonishing to see how much light can be brought in with the best of these. I like the large rectangular style.

best, andy

[Geoff S.]

Hi, Andy;

Good info on the Dow Corning 791/795. I'll look for it. What benefit does a secondary frame give, or conversely, what syndrome does it avoid? If your prism doesn't come with a frame, do you fabricate two frames?

Geoff

[Terra Nova]

Originally Posted by Geoff S.

Hi, Andy;

Good info on the Dow Corning 791/795. I'll look for it. What benefit does a secondary frame give, or conversely, what syndrome does it avoid? If your prism doesn't come with a frame, do you fabricate two frames?

Geoff

Yo Geoff,

here's a link to the supplier of the ones I've installed:

Marine Skylights

the 3X10 rectangular prism, same as used on the Mason 43's.

After letting this into a deck, there is sometimes not enough material left to provide sufficient support, so I fabricate a frame, which also provides a finished interior trim.

best, andy