Speaking only in schematic form, and offering no structural advice or endorsement, I agree with Mark's concerns about safety, and offer the following comments:
From your description, I think you are considering building walls of 2x4 6" on center, 20" high, to be placed on the outside walkway between the wood nose rail and the cabin wall. Beams extend across the walls, through the windows, outward beyond the wall far enough to port and starboard, to achieve a triangulation kicked back to the wall.
Doing so would place some bearing on each side, down onto the port and starboard walkway, but naturally most of the lifting weight will be lop-sided to port or starboard, down onto the walkway closest to the motor (unless you plan on using a column at mid span, extending down to the keel area, to cut the span in half, in which case, the walkway takes half the load, and the column would take the other half).
As Mark noted, the span of your unsupported beams will be in the 10 or 11 foot range, as I understand your plan, with a 30" overhang beyond the wall in order to achieve kickers back for triangulation (using 16'lumber). I question the ability of the 4 2x4s making up your 10 or 11 foot span to hold the weight.
I also question the ability of the outside walkway to hold the weight being transferred to the bottom of the wall. Mark noted the potential for cracking of the fiberglass walkway. If the motor weighs 800 pounds, and your system puts half the weight on the walkway, it's the equivalent of two 200-pound guys standing there. Whatever system you elect to use, you should remove manifolds and transmission, to make the object you are lifting as small and light as possible.
On my recent Sea Skiff project, my engine lifting weight was transferred down to the ground by 4x4s, and a beam made up of two 2x8s spanned all across the boat (about a 10' span). I had nothing bearing on any part of the boat. The system I built worked for a small block with no marine manifolds or transmission, but I could sense the weight was significant. In reality, assuming the bare motor weighed around 500 to 600 pounds, there was probably around 250 to 300 pounds being transferred down each 4x4 column to the ground. Everything was triangulated and stayed, to prevent sideways racking longitudinally and laterally.
For use as a beam, 2x4s dont have any strength laid flatways on a span, and not much even when stacked 4 high flatways(around 5-1/4" overall height)because they all want to bend together on the weak axis. Putting them on the strong axis, side by side would appear better, but I still question this on a 10' unsupported span. For any such schematic of this kind, a 4x4 column extending down to the keel or motor stringers at mid span, would make that overall span of your beam more like 5 feet(it could also be triangulated with a kicker).
In addition, the term "2x4" includs, SPF (spruce, pine, fir) as well as structural straight grain yellow pine. The latter is MUCH stronger.
It is impossible for us to know the
exact conditions of the boat or design of the lifting system, fastening system, or lifting technique, sitting hundreds of miles away looking at a computer screen, so the only real "advice" given here, and support to a fellow boater with a serious task at hand, is to echo the concerns for safety and echo the idea of buying an engineer friend a beer and having him take a look at your conditions before attempting a lift. Hopefully the advice you get will be better than what you paid for, lol!
If I were on site, I would gladly give you a hand, and help with the work. As it stands, all I can do is express a concern for safety and caution. Motors are lifted out of boats all the time, people find various ways to do so, so please proceed with caution and be safe. Good luck, hope it all goes according to plan.
Regards,
Paul
Jerry, due to the fact that this forum gets world-wide exposure, I am adding our standard note for these sorts of things here, as a precaution, not just for you, but for anyone else in the future.
edit comment:
Due to obvious liability and safety concerns, nothing in this post or those that are associated shall be construed as a structural suggestion, recommendation, or endorsement, from the Chris Craft Commander Forum, Inc, chriscraftcommander.com, or any other participant here on the forum. We place this notice here in the interst of safety and caution, and by doing so encourage each person who is contemplating a lift of any kind, to use their own best judgement, not rely on anything posted here, and get professional help if necessary.
Thank you for your understanding,
Paul, forum host