Repowering a 54' Donzi Sportfish

PB - Is my math correct that using the 2.75" shafts with 1.97:1 will give me an actual safety factor of 4.9177 ? I just did a simple % take off from what you provided showing a 2.796" shaft needed to get to a 5.0 safety factor.

Thank you PB!

Here's my next dumb question: Does it matter which side of the helm I put the new engine/gear controls? Existing set-up is the old style with gear selector on port side and throttle on stbd side. I never use throttle during docking, just gear selector. We installed the BT controls near gear selector as that made the most sense to have close by. I'm used to standing to the port side of Capt's chair for docking as this also improves line of site as I'm looking directly through the flybridge door opening which is to port and my pier is to port.
The new controls will be a single head with gear selector and throttle in one unit. I usually see these mounted to the stbd of the helm. I would prefer to mount on the port side. I would rather have it convenient for docking maneuvers and just get used to using my left hand for throttle instead of my right. Most times I'm using throttle the engines will by synced and I'll use the single lever for throttle on both engines. I could mount it to stbd and move the BT controls but that isn't going to help with line of sight. Thoughts and input appreciated.

I visited ZF and got to operate the display of the Smart Command unit and got a full run down on it by their tech. I was very impressed and glad we selected this system. I will be installing the control head to the left of the helm as this just makes the most sense for our overall configuration.

The boat was docked yesterday, bottom washed and then got moved into the building this morning. The cradle was lifted off the transport carts and set in final location where the work will be done. She is all leveled up and ready for the real fun to begin.

Making some progress. Aft bulkhead access cut is made. Port side salon floor access cut made. Port gear and 8kw generator removed. Next is to slide port engine aft and lift up and out. Then the stbd side gets tackled. Still lots of hoses, cables and junk to remove then degreasing, cleaning and painting. In the photo looking down thru the access cut you can see the water maker panels, filters and pumps on the bulkhead. That's all coming out too.




up it up and out.

I bought the engines, gears and controls from a CAT dealer we have a commercial relationship with. I was given a substantial discount because we do lots of business with CAT and ZF. Part of the discount is predicated on non-disclosure. Sorry. I bought generators direct from Northern Lights. Same situation as the engines and gears. I'm sure your local CAT dealer can quote you easily enough, nothing exotic here. But I will tell you, discount or not, this stuff is expensive.

My boat has only ever had 12v and 24v. I have no 32v. I'm staying with the same set-up so need to change any chargers or toilets.

I'm not expecting any significant gain in cruise or top end. The hp is about the same, only a slight increase. The weight savings should be in excess of 2,000 lbs all in so that will gain me some. I'm also changing gear ratios and props so might get a little efficiency there as well. If I gain 1-2 knots I will be happy. Where I do expect to gain is in having the confidence to run these new engines at 80% load for cruising. Whereas my 12/92s ran well I never felt comfortable at 80% and usually cruised around 72%. Based on fuel curves I should be able to run the C-18's at 80% and burn roughly the same fuel the 12/92s were using at 72% - around 85 gals/hr total. If this turns out to be true then I expect to be able to cruise at 3-4+ knots faster at 80% load then I was achieving at 72% with the 12/92s. I'm trying to keep my expectations conservative so as not to be disappointed. My main goals are not related to speed and fuel burn so any improvements here are just extra benefits.

First engine is now out and on the shop floor. We elected to lift it with chain falls to the salon then rolled it out on Hilmann rollers riding in steel channels. This allowed the aft bulkhead opening to be smaller as we didn't need room for an overhead trolley or stinger. This also kept the rolling mass center of gravity at a much lower point. Finally, this also allowed a much more controlled movement which we felt was also safer. The channels are supported by 4(ea) 12x12 beams spanning across the cockpit and blocked to the shop floor. This means no load whatsoever on the cockpit deck which we preferred.

Stbd engine came out today. Still have 20kw gen, old water maker, oil change pump and misc cables and junk to remove. Then ER will get deep cleaning and paint. Then we go into new install mode. I’m anxious to see things start going back in.
I placed final order today for 2.75” shafts, couplings, Veem interceptor props, Lasdrop seals and Duramax cutlass bearings. I hopefully got lucky and do not have to line bore struts or shaft logs. Existing bearings for the 2.5” shafts are 3.375” OD, The same OD bearings are available for 2.75” shafts from Johnson Duramax. However, my lead tech still wants to shoot the alignment between struts and shaft logs. He said if they are not 100% deadnuts he will take a minor bore cut to correct it.
I still need to make a decision on new water maker. I’m leaning toward the Bluewater units. I’m also debating if I want to order the remote handheld engine controls but I just don’t think I’ll use it. Although it could be handy to have up on the bow for when I’m pulling anchor from 300+’ depths. Would save the trouble of hand signals to someone on the bridge. But the hand signals are pretty simple.
Also researching and looking at various line cutters to put on the shafts. Never had a problem but I don’t want any either. I have had a few close calls. My goal is to never have to use my wetsuit and dive gear in that cold water . I’m leaning toward the Shaft Razor disc style cutter.