Buying 54' Donzi

Hi there,

First of all, best of luck on your new purchase.

Regarding the gap between the struts and props, I have heard that many many times that it should not acceed twice the diameter of the shaft and it is better when it is the same diameter, apparently because then it will cause vibration and loss of speed. By practical experience, I never had ANY boat that was less than twice and never had problems with vibration (needing to change any part before its expected time) or loss of speed. The only thing I can agree with is that if you are looking for pushing hard on the throttles to juice more speed fast then you might effect the parts but after all this is a sport fisher so even under tournament conditions it won't be pushed as ruff as sports or speed boats are pushed, specially that you will not be trolling in slaloms at 30knts!

Again, good luck and happy fishing.

Cheers!

Good point, I will consult a friend, (a boat techy), and even see if a blueprint is available to check the angels and dimensions.

Cheers.

Engine survey

This may be stating the obvious as you may already be doing far more than the oil analysis on the engines, but just in case:
When I purchased my Hatteras with fullly over hauled 12V71N's, I asked for a full engine survey and was very impressed with the surveyors work.
He used a fibrescope to inspect the cylinders in the air boxes, checking to see that there was not too much scuffing by viewing the cross hatching. The oil analysis was also done, however it doesn't really tell you too much unless there has been a serious issue or if the oil was recently changed.
Worth the extra dollars for peace of mind.

I can tell you for sure that mine are differently not that much. Doesn't that boat have 3" shafts?

Somehow it seems strange that there are 2.5"s there- I have the 16-92's in a 65 and have 4 inch shafts and B Roscioli "overbuilt" his boats. At 1450 HP I don't need any more than the 3 inch shafts. Even 3.5 would be more than enough- which leads me to believe you have 3 inch shafts.

On the shaft overhang I just had my shafts shortened last year. I also had shorter prop hub than I was supposed to have. Mine were 5 inches on one side and just over 6 on the other. The previous captain ran aground and the shafts were changed (I think) and the rudders were (I know). The shortening did cut down on the cruising vibration. I also have the Japanese twin disc copies for gears which have a 2/1 ratio- that itself make vibration at 2/1. Do you have Federal props? You may have those with a shorter prop hub and could buy props with a larger hub to cure any issue you have instead of cutting the shafts down.

In any event I would worry more about vibration than a shaft breaking at the taper.

Except 12v92's after the first 200 hours are more like 950hp...... Every boat I've ever run with 12v92's seemed to have lost 200hp somewhere after the first 200 hours and had to have the props cut.....from then on out they stayed the same, even after majors they stayed the same......

You should have 3" shafts in that model. Mine came with 3" and don't see any reason why Roscioli would have changed.

Take a hard look at the rudders on that boat mine had to be replaced with stronger models made by Western Branch Metals. The original ones where made very thin, knife like and had issues with vertical cracks near the rudder stock. But that said they where not designed to run at the speed my boat is now capable of doing. And I never noticed the cracks till a year or two after the re-power. I know Roscioli redesigned them but I don't know if that was done on the 54's or not.

That seems very un-donzi like.

Congrats are in order then, best of luck with it.

Cheers.

No, if the shafts are properly sized for the horsepower, then I don't see any reason that would be a deterrant.

Looking back though an original brochure it says that the 2.5" shaft was standard with the 12v92 engines.

Good luck with your purchase

I own a 65' Donzi and just finished up rebuilding the entire machinery space. Based on my experience with my Donzi as well as others that I'm familiar with, I thought 2.5" seemed a bit undersized. Regardless, congrats on the purchase.

It all depends. The smaller the shaft, the less drag and theoretically more speed. I worked on a 75' Jim Smith with 2000hp 16v2000's that had 2 1/2" shafts, but they were a special shaft that was splined like an outboard and didn't have a keyway, making it stronger for it's diameter.