25 Seafari Repower Question

[FLexpat]

Originally Posted by FLexpat

I think Bilgerat had 6-700# in the bow to make up for the CG issue with the bracket and twins. I made a rough 3D CAD model of the 25 and calculated the CG shift between a single I/O and twins on a SS bracket - I don't remember exact numbers but remember it was surprisingly large and that Bilgerat's bow ballast didn't even make up for it. I will try and track that stuff down.

Found some files:
Bilgerat used 400 lbs in the anchor locker to get the CG almost to where it should be. Twins on the bracket shifted the CG aft about 40" - likely much more since I estimated bracket weight as 200 lbs (I used FG); far less than it really is. With the 400 lbs in the anchor locker and the 'light' bracket it was still a couple of inches aft of where it should be. If the ballast is in the cabin bilge, lots more is needed.
Like Connor said, the OBs raised the CG a good bit relative to a single I/O (350cid) and ballast in the anchor locker didn't really help that.

My personal opinion for the 25 is that a conversion to a CC with an alum block L83 or L96 under the console jackshafted to an I/O would be perfect but it would be kinda needy on the maintenance side.

Hope this helps.

[SeaRiggs]

Thanks Everyone!

This is great info.

Let me get to work on all this and I'm sure i will be back in touch shortly.

[FLexpat]

Pulled up files and ran a couple of cases. The hull model is the same for all of them; rough approximation of the 25 and a Corecell transom (~80lbs less than marine ply) w no rigging, fuel tank, or seating. Since we are talking about an OB conversion, I don't show a view of the single I/O but I do have a grey circle on all of them where the CG is for that configuration (5.7/350CID). The vertical line is where BigFluke found the best fore-aft CG to be.
EDIT - CORRECTED WEIGHTS
Something was bugging me about my first set and when I looked at the numbers for Connor I realized I had labeled 400lb weights as 200lb. I have corrected the text in these images.

[SeaRiggs]

Wow..Pretty work Mitch!

Thanks for posting these.

This is a great starting point.

Much Appreciated!

[cdavisdb]

25s are rare birds. Where did you find yours?

Flexpat, thanks for the pics, confirms my feeling about how my boat handles and its desire for more a bit more weight forward.

[FLexpat]

Originally Posted by cdavisdb

Flexpat, thanks for the pics, confirms my feeling about how my boat handles and its desire for more a bit more weight forward.

Just ran the numbers and it looks like yours would like ~150lbs under the cabin sole just fwd of the hatch to the foredeck.

[cdavisdb]

I've found that moving a heavy diver from the engine box to the fwd bulkhead makes the boat perfect near the end of the trip when all the water stored under the berth has be used. About matches you numbers. Surprising how much difference in speed that creates.

[SeaRiggs]

Originally Posted by cdavisdb

25s are rare birds. Where did you find yours?

Flexpat, thanks for the pics, confirms my feeling about how my boat handles and its desire for more a bit more weight forward.

I found mine in VA.

Once I figure out how I am going to account for the necessary added ballast, I'll get to work.

I certainly appreciate all the feedback and details.

[Bigshrimpin]

I wonder if you could just make a compartment along the keel in the bow for 400lbs of lead shot (or never ending supply of 8 - 16oz sinkers)

[cdavisdb]

If you are going to use ballast to make the horizontal cg work with outboards, think about total weight. The 25 is narrow and super deep. Adding weight makes a considerable difference in load on the engines and fuel economy. In mine, the difference between a full load Bahama trip and light load camping trip with me and my wife is substantial.