Hull extension planning - HELP!

[jgdyer]

I'm getting ready to repower my 1960 Marinette 29' aluminum cruiser with twin outboards, and I have some decisions to make ...

I have attached 7 images to illustrate ...

My pal Steve and I spent some time reviewing the modifications we made 15 years ago to accomodate Sea Drive power ... We believe that, despite the poor choice we made to stiffen the transom with 3" of marine plywood, all our bracing and monocoque are sufficiently durable to handle dual engines on a bracket ...

So, I could let D & D Marine build me the version you see in images LONB-1.jpg through LONB-3.jpg ... Cost around $2,000 ...

However, I would be shifting quite a lot of weight aft ... subtract 680 pounds for the seadrive & 135 pounds for the 25 horse kicker, add 150 pounds for the bracket, add 850 pounds 30" further aft ... And although D & D's bracket provides some flotation to compensate, Galatea only draws 8" at the transom today ... and D & D's bracket stops short of the bottom by a good 2" and doesn't span the full beam ...

I haven't done much math, except to calc that a fully realized hull extension gets me approximately 700 pounds new flotation ... I am guessing that D & D's design will provide much less ... So, in a following sea, I might find that the boat wallows enough to sink the engines and stern ... Causing undesirable results ..

Or do I worry overmuch?

If not, then I should undertake a more flotatious path .. But I have three choices, at least, to consider in a hull extension ...

On Galatea, the chine angles down relative to the keel line ... If I simply extend the chine and keel lines aft 30", they conspire to leave me with zero deadrise at the transom ... As I see it, I can do one of three things ...

In Aft Detail2s.jpg I maintain constant deadrise from the "old" transom to the "new" transom by angling the chine line upwards at the junction.

In Aft Detail3s.jpg I essentially clone the last 30" of the hull (including the variable deadrise and chine angle) and splice the clone on to the back ... This produces a step in the chine and the hull at the junction.

In Lifetimer Bracket.jpg I copy their scheme which appears to solve the chine issue by abbreviating the cross section beam-wise ... (Did that make sense?) However, this trick robs us of flotation ...

Composite Dimensioned Small.jpg shows you what the whole boat looks like ..

Suggestions?

Thanks!

John Dyer