Request for assistance for the installation of two Sterndrives?

Hello everyone, I'm new to this forum. I am currently in the process of building a new boat. I have not been able to find any relevant information on this, so I want to consult you here as well.
What do you think the distance between the two Sterndrives? I also attach a file with the main parameters.

 

Have you asked the supplier of the sterndrives?

 

It will depend on the make and model of the sterndrive. Also, the engines will need access in between for service and repair. That is one dimension many boat manufacturers ignore.

 

I'm sorry, I missed it. The sterndrives will be Mercruiser Alpha 1 G2, Mercruiser motors 3.2L 230 KS. My designer recommends that I be guided by the size of the engine, with the engine being 690 mm wide and the distance between the engines being 500 mm. But I'm not sure if this arrangement is good and whether there is any dependence on the location of the boat's behavior. Control, stability speed.

 

http://www.ta-group.at/dokus/service manual _14 alpha i gen ii outdrives 1991 to present.pdf

 

Looking at the rear profile of your transom, I would either remove the two inside lift strakes near the keel or at a minimum taper them from the transom forward 4 - 5 feet. You want the water coming into the prop
as "clean" as possible.

The information that you "could " be looking for is on page 6A-68 that refers to the tie bar length. Of particular note is the existence of two tables dealing that offer two sets of centerline values depending upon which side the steering cable comes into.

Also, your "designer" should be reminded that before he designs the interior hull bottom
reinforcement, ie the stringers that he has the proper spacing for the engine mounts, clearance between and the height. This will permit designing the stringers to suit the
engine space requirements and motor mount widths to suit the engines. You would not
have to remove some structural stringers, for engine clearance and install engine stringers in the proper space.

While this maintenance manual is full of information, I did not see any reference for the
measurements from the bottom of the hull to the centerline of the drives/transom mount etc.

This will vary with deadrise to ensure that the ventilation plate is at the correct
elevation wrt to the bottom of the hull

While Gonzo's link shows maintenance and repair in detail, Mercruiser will have an actual Installation Manual that will walk you through the dimensions of the engine mounting and required clearances. VolvoPenta has them for their engine/drives and additionally, they covered a myriad of other aspects of installing an engine. Engine room ventilation, fuel systems, filters, mounting methods, and the list went on.
IF you are actually going to build a boat, then you NEED this set of instructions.

You designer should have let you know this or at least recognized that there is more than one important measurement than centerline distance

 

You also need to consider how the boat will behave on hard turns. If the sterndrives are too far to the outside, they may come out of the water. That will cause the boat to get out of control and also damage one engine.

 

Doubt that boat will be doing any crazy banking, but the strakes seem superfluous closer to the centreline.

 

Installation. Aquamatic DPH, DPR Volvo Penta IPS Inboard D4, D6 1(1) - PDF Free Download https://docplayer.net/65018256-Installation-aquamatic-dph-dpr-volvo-penta-ips-inboard-d4-d6-1-1.html

This installation manual is a little different than the one that I have but it appears to have the same categories
While this is not the proper one for your intended engines, there is very pertinent information sections that apply pretty much to any install. Fuel systems, sound proofing, ventilation, etc that will be of assistance
Mercruiser will have the same one as they need to ensure that their installers are installing their units correctly

 

don't worry, you're in good company:



So long as they don't knock into each other and are linked, hydraulically/mechanically - I've never encountered issues. Seems these guys don't worry either!

 

We installed a lot of these Volvo stern drive in our patrol boat. Should not be a problem between the center to center distance as this is not a ship with big propellers. The center to center distance will be dictated by the width of the engine and the serviceable space between them. Of course, this will be dictated by the positioning of the engine bed/cradle that will align the engine to the transom spacing.

The bigger problem we had is that the fiberglass transom we had is not perfectly flat and perpendicular to the boat's centerline. We had some problems adjusting the trim as shown in the manual.

 

Many thanks to all for the answers and advice you have given me. As well as the installation manual helped me a lot. when i'm ready i'll show pictures how i did. Оnce again thank you.

 

You need to get your hands on the exact installation manual for YOUR drives as it appears that Merc has two different measurements depending on from which side the controls come into the drive. And you have to co-ordinate the
stringer location in the design to match the center to center spacing or you will run into lots of problems when you get to want to install the systems.

The height, width, shape and clearance between the stringers need to be designed into the hull pivoting on the spacing of the drives and engines. AND also the transom shape, angle etc where the drives penetrate transom. The shape that you have drawn does not seem to be a workable profile.

 

I guess this kind of difficulty is another nail in the coffin of sterndrives, versus big outboards.

 

Not really. This is a problem with the designer, not the equipment type.