Hi,

I´m in the end of building my own home made 2x surface drives with most of the joints/length measurements from "ASD8"
As I understand Arneson runs with a separate hydralic trim circuit with it`s own electrical trim pump and a engine driven PS pump/hydr. helm system for the steering cylinders, fine so far.

When I draw this geometry up in the CAD I can see if you trim up the drive tube let`s say 10deg, the steering cylinders must be shorter and vice versa when you trim down.
This is not a problem if you run a single drive with a single steering cylinder, the drive will just make a "C" shape travel trim vice seen from behind.

But I will run with 2x drives, 2x outer mounted steering cylinders and a "solid" tie bar, as many Arneson applications do.
As I see it, it will be a problem as you have high pressure oil in the steering cylinders holding against this action, so my question is how can this work...?

I assume you just don`t want to use the trim cylinders as a "override" and just force the steering cylinders to change lenght, this will put in huge load in the transom.
Is there a oil relief valve somewere in the steering circuit, between the steering cylinder chambers..?

I really like to get some info regarding this, thanks!

Best Regards
Richard Adolfsson
Sweden

Hi,
The lamp just turned on over my head and I just realised the answer to my own question:

As the steering rams are cross conected and the Left/Right connections on the hydr. helm is closed with no steering wheel input, the steering ram oil will just flow over to the other diagonal steering ram chamber, easy ;-)
So when you trim up or down the steering rams will just help each other to ger longer/shorter due to the geometrical "issue" and the only load you put in to the transom for this is the force it takes to move the amount of oil cross vice steering ram chambers.

So now I can just continue with life as usual.

Regards
Richard

I had to think about it for a minute - you need to account for the piston rods. They change the displacement of the overall system when you trim.

Yes there is normally a cross-over relief valve.

a note here from an asd8 user is you do not trim like a regular boat the faster you go the more you put the drives down to keep the right amout of prop blade in the water as the hull lifts up (V hull) it also upsets the boat to move the drives at hight speed so you kinda set the drives at where they need to be for the speed you want to go and drive it up to that speed with lots of power

Thank you for very valuble input, I forgotten to count the rod ;-)
Yes, I will run this on a 24deg V-bottom hull.

Interesting about the cross-over relief valve, where do I find them..?
Anyone who have a picture from such a boat?

@boost bros, do you have such cross-over relief valve on your ASD8 setup
Quite strange they are not mentioned in all the aftermarket "Bravo external dual ram kits" as far as I can see?

Regards
Richard

We need pictures!!! I always love seeing stuff built by people! Their creativity amazes me

I have think same question. Moving cylinder rod volume must go to reseivoir, otherwise something rip out from transom. If fixed end of all cylinders are in exactly same line trim should not move steering cylinders at all but it's very difficult get geometry so well, maybe impossible.
I have original Latham steering in my 47' Fountain, there is strange aluminium block in engine room where all steering hoses go. Is it some pressure relief valve?
I do also homemade surface drives to Fountain. It would be nice change pictures and information.
You can look my project in restorations page.