Transom cutout required for Two outboard motors

[D Gobby]

I'm in the process of thinking about my next build, a Tolman Skiff.

I've been thinking about the Transom cutout required for two outboard motors.

My thoughts are of running a 115 hp outboard for the main and a 8-9.9 hp outboard for the kicker both mounted on the transom.

It appears that the main would require a cutout of 30 inches, this should allow enough room for full range of motion for the main, in both the operating and tilted positions. My thoughts are to offset the kicker 30 inches from the main to allow both motors full independent range of motion. I'm also thinking of offsetting the main to starboard 10".

Since the kicker will, in all likelihood be tilted up manually, how much room is required to allow the kicker to have full range of motion while in the operating position.

I could make both fit in a 60" cutout, but I would like to keep the cutout to a minimum.

Does anyone have any thoughts on this.

Darrel

[htom]

I'm inclined to think that you should not offset the main at all. I think you'll have handling problems if you do (at any speed higher than you could row.)

[D Gobby]

htom
Many of the Tolman skiffs that have been built have the main motor offset 10" from the center line. From what I understand those that have the motors offset report no handling or trim balance problems.
I guess my question should have been, what is the min transom cutout required for a kicker motor in the 8hp to 9hp range need while the motor is in the operation position, to allow the kicker motor full range of steering.

That should make things clear as Mud!!

Darrel

[Andreas Jordahl Rhude]

I have two 1957 Johnson 35 HP outboards on my Thompson. The transom cut-out is about 38 inches in width. You can see pictures at www.freewebs.com/thompsonboat/index.html

Andreas

[BrianW]

Hope I don't get Scotted for posting these pictures, but it might help. My kicker is mounted on a bracket so it is located slightly aft of the main, as seen in this picture...

http://img.photobucket.com/albums/v136/BrianW/Honu/suzukiathomeinthesnow.jpg

Here's a closer view, I should mention that the kicker is in this position when running, as the kicker throttle handle doesn't quite clear the top of the transom if I have it turned the other way...

http://img.photobucket.com/albums/v136/BrianW/Honu/suzuki175hungontransom2.jpg

The boat is down in the slip now, but tomorrow I can go take some measurements between the engine centerlines if that helps.

[Tristan]

Just curious, as Tolman gives fairly specific suggestions for power for his various sized skiffs, what size skiff are you contemplating powering with the 115 hp motor?

[ahp]

I haven't seen the plans but 115 hp seems like a lot for a skiff. Will you build a bulkhead, rail high, ahead of the OB? That can be a life saver, to prevent flooding the boat through the transom notch. A lot of lives were lost because OB boats didn't have that feature until the US Government held the builders feet to the fire and made them do it.

[Krueg]

Why not just put the kicker on a bracket? Seems like the most logical solution. I sure wouldn't want a 60" cutout in the transom of my boat. Plus, offsetting the main seems unnecessary and unnatural.

I totally agree with ahp about the bulkhead. I've seen outboard boats that would be swamped by a halfway decent sized wake, not to mention a following sea.

[Old Salt]

Renn doesn't do anything "mainstream"...that is one of the reasons that the boat has been so successful. I am building an 18' Standard with the offset motors. Reports from other builders are that the offset does not negatively effect performance. In Alaska there area LOT of the boats (with offsets) operating for both pleasure and commericial use. This is probably the worst place to discuss things that are not mainstream. You should go to the Yahoo Tolman group (http://groups.yahoo.com/group/tolmanskiff/)and get information straight from the boat owners who have built and used such a configuration.

The offset motors have some advantages...both motors (main and kicker) are mounted exactly at 20" (one motor is offet 10" to port and one 10" to starboard). You dont have a motor bouncing on a bracket when you are trailering.

If you have a proper splash well, who cares how wide the transom cuttout is. I am building a full height splashwell with 2" drain holes. If you take a big wave over the transom, most of it will run over the top of the transom cuttout...the rest will drain throught the holes.

There are builders on the Tolman forum who have built Jumbo's with the main motor set on the centerline and kicker off to the side. Go to the proper forum and ask your questions there. They are very helpful!

[BrianW]

Well, just in case the original poster comes back... turns out it's about 30 inches between engine centerlines...

http://img.photobucket.com/albums/v136/BrianW/Honu/P1000948.jpg

[D Gobby]

Thank you for taking the time to measure the distance between centers for me Brian W. My thoughts were that the distance required between center's for independent function of both motors needed to be about 30" your measurement seems to confirm that.

I have posted this same question over on the Yahoo Tolman site and I'm still waiting for replies.

Darrel

[G Jacobson]

I'm probably just muddying up the water some more, but I've had similar issues figuring out the outboard well and transom on my boat. Although it's not a Tolman, the hull cross section at the transom is almost identical to a standard. I designed my boat with the intent of using 25-40hp 2-stroke twins. For that reason, I angled the sides of the well outward slightly to better accomodate the motors. Also, the sides of the well are low enough to allow the outboard "heads" to swing into a splashwell area aft of the "internal transom". I'm hopeful that these accomodations will provide good following sea protection while allowing the twin motors full range of motion. Unfortunately the boat is still unfinished and the design untested.

Here's the basic dimensions of the outboard well and transom:

http://i9.photobucket.com/albums/a68/SilverFly/TransomDrains.jpg

Also, may be interested in a post I made seeking advice on setting my boat up including some useful suggestions on the transom and motors:

http://www.woodenboatvb.com/vbulletin/upload/showthread.php?t=54417&highlight=center+console