F.4.1 (Boom extrusion) Materials

[MattAdministrator]

Does anyone know what aluminum alloy HV-90WP is? It is specified in Etchells Class Rules F.4.1, and other sections.

F.4.1 MATERIALS

(a) The spar shall be of Aluminum alloy to specifications 6061-T6 or HV-90WP or equivalent.

I cannot find the HV-90WP alloy designation referenced anywhere. The HV-90WP should be eliminated if it does not add meaning to the requirement.

Also, technically, 6061-T6 is not a specification. It is just an alloy designation.

Also, World Sailing’s Equipment Rules of Sailing (ERS) defines “spar” as the entire boom including fasteners and fittings, but excluding running rigging. So, while the ERS still may not be 100% clear on the scope of a “spar,” if OD Rule 4.1 is taken on face value and interpreted per the ERS, anything that is not AA6061-T6 on the boom is illegal. The end caps are probably a different alloy, suitable for casting. Obviously, the rule needs to allow (316 and 304) stainless steel parts and fasteners, and various “plastic” parts, and maybe even some wood parts. So, OD rule 4.1 needs to be rewritten so that it clearly states that just the main extrusion is 6061-T6. Maybe also the doubler sleeve should be the specified to be the same material; or has the class opened that piece up to other materials? No doubt, if a spar builder is fabricating the doubler sleeve from a round aluminum tube, that tube very possibly is not 6061-T6, very possibly much weaker (but more readily available) 6063 alloy, or even something completely different.

[MattAdministratorAdministrator]

Just to add more information in case it comes up… We may not need to go to this level of detail, but maybe someone in the ODTC should know which spec(s) the spar extrusions comply with. Following is the list of Aerospace Material Specifications (AMS) for AA6061 (taken from U.S. DoD MIL-HDBK-5J) and the structural shape(s) to which each spec applies.
AMS 4025 – Sheet and plate
AMS 4026 – Sheet and plate
AMS 4027 – Sheet and plate
AMS-QQ-A-250/11 – Sheet and plate
AMS 4115 – Bar and rod, rolled or cold-finished
AMS 4116 – Bar and rod, cold-finished
AMS 4117 – Bar and rod, rolled or cold-finished
AMS-QQ-A-225/8 – Rolled bar, rod, and shapes
AMS 4150 – Extruded rod, bar, and shapes
AMS 4160 – Extrusion
AMS 4161 – Extrusion
AMS 4172 – Extrusion
AMS 4173 – Extruded rod, bar, and shapes
AMS-QQ-A-200/8 – Extruded rod, bar, shapes, and tubing
AMS-A-22771 – Forging
AMS 4080 – Tubing, seamless, drawn
AMS 4082 – Tubing, seamless, drawn
AMS-WW-T-700/6 – Seamless drawn tubing
AMS 4127 – Forging
AMS 4248 – Hand forging
AMS-QQ-A-367 – Forging

[MattAdministratorAdministrator]

After a little more searching, the HV-90WP possibly could be a hardness measurement. A hardness measurement can be used (in conjunction with other more complicated tests) to verify that an alloy is what it is supposed to be. So, maybe the HV-90WP is not an alternate alloy, but a qualifier for the specified 6061-T6 alloy. The specified designation (HV-90WP) is not one I have found, but it could be a format used in the 1960’s when the rules were first written, but which has since changed. There is a hardness designation called a Vickers Hardness, which is abbreviated HV, and it has a value of 107 for 6061-T6. Maybe one of the class graybeards has some insight.

[MattAdministratorAdministrator]

For more on the Vickers Hardness Test see link at: Vickers Hardness

If this HV-90WP designation refers to a Vickers Hardness test, the 90 and the WP codes are still a mystery.

But, another way to consider this is since the boom (and mast!) must be obtained from a licensed spar maker, why do we need this requirement at all? These requirements should be in the super secret Etchells Builder’s Specification.

[Author]

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