Engine rebuild to factory spec may set one back about £1,8 - £2K per cylinder ... so £34 - 35K plus removal/install (removal should be OK on a Hatteras as I believe there is a hatch above each engine for that purpose)...
Sounds a little bit like a hull with superstructure re-built as most of the Jupiter 40's registered in the Jupiter club in Denmark are of the more traditional Jupiter superstructure lines ... You may find more info on their site ... or to raise some questions.as Lady Marie is recorded as being...
AQAD32 ... parts are not readily available ... Family friends bought same boat new with same engines in 1977 ... lasted a couple of years, weak cylinder head seal and boat did struggle to get up on the plane if you had anything heavy, such as a dinghy, near the stern... 12-13 knot cruise when...
Presumeably the "500" refers to a size measure, so let us assume that is 1/2 liter internal volume. @ 200 BAR, that equates to 100L.
Assuming we (at rest and at surface level) exchange approx 0.5L at a rate of 12x each minute which gives us a consumption rate of 6L/Min and triple that with...
At 625HP, your engine cannot be a 6V71 !! The only engine at that rating was a 6V92 DDEC with electronic governance and injectors ... so what you will need to look for is a engine with that name/code combination ...
Such as... Detroit Marine Diesel Engines pair 6V 92 TA DDEC 625 hp 24 volt...
Check the exhaust bend (where coolant meets the exhaust gases) ... easily gets clogged up by rust etc., and restrictions there will have give similar symptoms ... simple to check and relatively easy to fit a replacement..... but do check that it is above water level before you undo the four...
String a fishing line from VHF antenna/arch/high point and forward .... preferrably in a X formation. Seagulls will not see line from high, but will discover something obstructing landing zone when heading for landing and veer off ... Not seeing the obstruction from a distance, but noticing...
15M powerboat will probably be too tall for the bridges, and with bonze props swinging at 1.3 M are highly likely to be dinged ... Land transport and plonk in sea in Netherland or near Cuxhaven for then to take through Kiel canal will probably be the fastest/cheapest combination ..