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I have a 1989 Montauk and noticed that the clamshell had badly corroded, so I wanted to replace it. After reading the posts about it, I could only buy a clamshell with 4 holes and the one on the boat has 6. I drilled out and tapered the other two holes, but then I finally noticed that the screws in my boat were pan head screws, and started wondering why the holes were tapered. My question is, are there supposed to be pan head (as mine are) or countersunk screws in the clamshell? Also does anyone know the proper size screw to use?

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That info can be found in our OEM Part Info and Photos section:
http://www.whalercentral.com/viewpage...page_id=69

http://www.whalercentral.com/photogal...hoto_id=32

and an article we have here in our Articles section:
http://www.whalercentral.com/articles...icle_id=52

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Thanks for the information, which I have already seen, but it doesn’t address my issue of the type of screws needed to mount the clamshell. I need to know if it is pan head screws or countersunk screws. Also, correction to my post, 3 holes in clamshell to be increased to 5 holes.

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Whaler always used phillips truss head #8 screws on clamshells. The chrome-on-brass Perko clamshell comes with three holes drilled. Whaler added two more holes. The Perko clamshells do not hold up well in salt water, and you might want to consider an identical clamshell in stainless.

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Perko now produces the traditional 2" clamshell vent in stainless. Exact same shape and dimensions as the chrome plated brass. Make a jig for the additional two holes and you will be set. Just installed these in my 1988 Outrage 18.

Finnegan is correct, Philips truss head #8 ( I believe 3/4" long). Truss heads have a larger bearing surface than standard heads, but not by much.

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Thank you that information, it was exactly what I needed. I can always count on the Boston Whaler Central family to help with the small and large issues!

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Contrary to what 2 others have mentioned, I have never seen a Truss Head Screw on any Clamshell Vent.
Maybe this is just one of those interchangeable parts from boat to boat or year to year?

According to the parts manual for the Montauk 17' and Outrage 22' as an example, they list these screws.
#82009800 Screw, #8x5/8"

See the Parts Manuals in our Download section if you are curious.

The Clamshell is countersunk for screws, why would they use a Truss Head?
I would think they would just use a standard hole with no countersink. Much cheaper and easier and no depth control.

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Joe: I have three Whalers with factory installed Perko clamshells over the sump drains. Two of the boats I bought new, and the third one only had 100 hours on it from the original owner, and all clamshells are installed with the truss head screws. The three hole clamshells have all been drilled for two more holes, and those new holes are not countersunk. Because the original clamshells were chrome on brass, countersinking the additional holes could not be done. That is probably the reason they used the truss head screws on all five holes. I also think the truss head screws are more likely to be watertight.

The boats with the truss head screws are a 1975 Outrage 19, a 1986 Outrage 18, and a 1989 Outrage 25.