Hydraulic steering: what pump/cilinder capacities?

Dear All,
I'm looking for a bull-horn type hydraulic steering system for my 115Hp Suzuki outboard, on my deep-V hull mobo.
What would be the minimum required helm-pump and cilinder capacities I should be looking for ?

THANKS,
V.

 

ᐅ Hydraulic Steering for Boats | Dometic https://www.dometic.com/en-us/outdoor/power-and-control/marine-steering-systems/hydraulic-steering

Here

 

Dometic/Seastar technical support is exceptional as well.

 

Was hoping to learn some -independent- rule of thumb on cilinder capacity per outboard power range.
I notice cubic inches for the same HP can vary significantly per brand.

 

That is true, however the Dometic site lists, if you drill down, the capacity of their cylinders and pumps, and makes recommendations based on your boat.

Dowload their pdf. It will tell you what you're looking for.

 

Hi Vronsky, from my personal experience with hydraulic steering (manual hydraulic steering (simpler one), not power steering), I think this is the order in which the simplest steering system should/could be designed:

1. Find the hydraulic cylinder that fits your required geometry (of course, something reliable and hopefully for marine use). This is the key point (type of mounting, stroke of the cylinder, etc., e.g. you already know that you need bull-horn type as you have stated). Selected cylinder will have some defined cylinder capacity. My wild guess is that when you find it, it will be more than powerfull enough for your need, no matter of engine power.

2. Find the suitable helm pump and steering wheel. Mind that the power required for steering is defined by the ratio of the helm pump capacity and the cylinder capacity. If you want more steering power, you need bigger capacity of helm pump, but this leads to more steering wheel rotations from end to end position and vice versa, if you want less rotations of steering wheel from end to end position, you need smaller capacity of the helm pump, but it will be harder to rotate the wheel. In addition, selection of the steering wheel diameter can also help to fight the force if required (think of a diameter as a lever).

3. Deal with hoses, fittings, mounting elements, etc. (sounds simple, but sometimes it could return you back to rethink step 1)

To skip math and more detailed explanation here about each step, I recommend reading the following links, which will give you enough knowledge to understand the whole system better and to calculate your wheel rotations when you have the capacity numbers of chosen cylinder, helm pump and known maximum angle of motor from end to end position. You could probably skip some of materials in links if you know what you need.
Marine Hydraulic Steering Systems https://www.sbmar.com/articles/marine-hydraulic-steering-systems/
Understanding Basic Marine Steering Ram Geometry https://www.sbmar.com/articles/understanding-basic-marine-steering-ram-geometry/

I think for deeper technical understanding, the previous link could be of help, but if not interested in that skip it and use only Seastar/Dometic documents and support, as stated by DogCalvary.

 

Pick the brand system you like and buy the kit with the helm, if you already have the ram just match similar displacements. 115 isn't a lot of horsepower and I'd think almost all the kits available in hydraulic should be able to handle it.

Inboards have almost countless options of rudders, tiller arms, rams and helm pumps. Outboards come in under 150 hp and over 150 hp. Step up to a bigger displacnt if you want more speed or do individual rams per outboard.

Only deviation we've done is putting the bigger hp kit on all outboards it can fit. But our outboards get used at high power in a static situation and seem to benefit from the bigger ram helm combo.