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nzjetboating.com Forums => Tech Library => Hulls => Topic started by: tyro on December 13, 2018, 09:53:18 AM

Title: gas struts for engine cover and sound deadening
Post by: tyro on December 13, 2018, 09:53:18 AM
Looking at gas struts for my engine cover. Cheapest stainless ones I  have seen in NZ are these are there better/cheaper options

https://www.absolutemarine.co.nz/gas-struts-stainless


Also what length of strut would I be best to use?

Also has anyone used this stuff to line an engine bay, https://www.motoquipe.co.nz/buy/dynamat-xtreme-trunk-boot-kit-sound-dampening-dead/10956?gclid=Cj0KCQiAgMPgBRDDARIsAOh3uyLzLsgje9a-BDow7CfQg11fX-FdFe-0lqf1ocVIU-rLQeT7z-6IaKwaAusuEALw_wcB

it looks like it has a good fire rating, not cheap but one of these packs would do my whole bay, I will put marine carpet under the bonnet/up front

Title: Re: gas struts for engine cover and sound deadening
Post by: JohnR on December 14, 2018, 07:28:59 AM
Gass strut length is relative to where your mounting points are and how much room you have, there's struts on trademe that do fine, don't think you need stainless ones.
Marine carpet carpet works great for sound reduction, that stuff you had a link to looks dear and heavy and probably isn't deigned to be wet,
How the project coming along?
Title: Re: gas struts for engine cover and sound deadening
Post by: Matthewf/Norbert/TuiDog on December 14, 2018, 11:12:40 AM
As the frequency of the noise we are trying to attenuate  is relatively low (engine noise, pump blades pass frequency etc) then we need a soft sound deadening material  that's itself has low a natural frequency.  So the soft foams are best which just happen to be cheaper.  Also nearly all of the noise we want to reduce will leak via just 12%  of airgaps!
Title: Re: gas struts for engine cover and sound deadening
Post by: Jeff B on December 14, 2018, 18:29:37 PM
If you are not using in salt water then General automotive has struts are fine. The seals will leak or you will bend them.before body dusts away. The better ones have thicker chrome on the shaft.
Length and strength vary so need to do some calculations on how far you want the lid to open. They are rated in Newton and 10n = 1 kg of force.
I generally use 200-400n.
This is a single 200n 125mm stroke on mu small boat. 2mm engine cover, pretty light.
If you cover is floppy then one each side helps otherwise it will twist.
Title: Re: gas struts for engine cover and sound deadening
Post by: tyro on December 14, 2018, 20:57:38 PM
Cheers will buy some cheap non stainless struts
Quote
How the project coming along?
super slow, bonnet done, security mesh sides beside engine done, new trailer under construction, wiring next
 
Title: Re: gas struts for engine cover and sound deadening
Post by: Paul on December 14, 2018, 23:15:37 PM
One point re gas struts: The rubber shaft seal, is internally lubricated with oil.  The shaft seal needs to be at the lower end/ bottom when closed, so that the oil stays on the seal keeping it lubricated.  If the strut is installed the other way up, then the seal dries and cracks, letting the 200Bar pressure out...