Hull Design Changes

Good Morning design forum. New member here who has found a great source of information. Thank You.
My building project & proposed changes are this. I have the bottom half of a 38' 1972 Chris-Craft hull (burned-out wreck). I have rebuilt the topsides F/G to a trawler design type, decks & superstructure are composite. Perkins diesel in place, no drive shaft or prop yet. What I am thinking of doing is cutting away some of the bottom stern & transom and re-doing into a small tunnel effect to accomodate a full keel, large (28") slow-turning prop, keel-mounted rudder, thereby also reducing some stern drag. Original boat was semi-displacement, now will be hull speed.
I am familiar with boat design to the extent that I am self taught and mathematically oriented, and will respectfully defer to any professional opinion. Thank You for your input.
Hank

 

What it sounds like to me, that you will also need to modify your complete engine beds and change your shaft angles. Was the hull rigged for single or twin motors? You say the engine is in place. IS it mounted to stringers in a single engine configuation? There will need to be a lot of hull structure in the stern to allow for this modification. Was or is the fuel tanks aft in the hull? You have surely taken on a big project.

 

Thank You Oyster. The 1972 38' Chris was a massively built F/G hull. Original configuration was for 2 engines aft of center of floatation mounted on 2 sets of stringers running full length of the hull. I used the inner 2 to mount a single diesel just forward of center. With a shaft length of about 14', shaft angle shouldn't be a problem. The hull, being a semi-displacement, has more hull volume aft than forward, and with the engine being moved forward, tunneling the stern would remove some of that imbalance. Those numbers I am still fiddling with, equipment placement, tankage etc. I think the real problem will be clean lines and smooth water flow to the prop and stern. By the way, old-timers in my area call the '72 Chris "the bullet-proof hull". None of this proposed work will be done till next summer, so I have the winter to play with the design. Appreciate all advice on this.
Thanks
Hank