Since I'm in lockdown I thought I'd play with some numbers in regards to the OP's situation.
Using Frank Butler's design displacement
(light ship???) of 10,200 lbs., LWL of 25' with a theoretical hull speed
of 6.7 kts and 21 hp at 3200 with a 2:1 reduction: the Catalina 30
needs all 21 hp to drive the hull
to 6.7 kts. It works out to be 501 lbs. per hp. In my opinion that's at the very top end of satisfactory weight to hp ratio, some would differ. Loaded with fuel
, stores and 2 souls the displacement
could easily go to 11,500 lbs. or higher. At 11,500 lbs. the hull
needs 23 hp to reach 6.7 kts and 565 lbs to hp.
My point with this exercise is to say it's probable the engine was worked very high in its power range during it's usage. At 11,500 lbs, using 75% of the engines power would drive the hull to 5.8 kts in calm, low wind
conditions. Some owners would be tempted to over prop the engine to bring the rpm
down at cruising speed making a marginally sized engine work
even harder in a high exhaust
temp condition. How bored am I???
On edit, Kubota, the manufacturer of that diesel, rates the D850 at 15.5 hp at 3000 continuous and 19.8 hp at 3000 Gross intermittent. And that's without taking into account hp lost
at the 2 shaft bearings on that boat but they do rate their engines spinning a fan so maybe a wash.