I am looking to purchase a 1980 30ft Catalina. it has an 11 HP Universal Diesel engine. The question is, do you think that 11HP is sufficient HP to move that boat against a tide or waves? Any guess as to top speed on a flat sea?
Something to keep in mind when you try compare boats and engines is that less than half of the boats out there actually have a Correctly-Pitched prop that will actually put All
he available hp to the water.
If this is the older Catalina with the engine under the port settee, it put the shaft near to being parallel to the waterline. That's more efficient than boats with a steeper shaft angle from an engine mounted further aft.
Another thing: the boat you are referencing is near in aux. power to the C-30's with the Yanmar YSM-12. It was also a great engine.
When people talk about having enough power to overcome a chop, OTOH, this is different than powering along in smooth water.
While a smaller engine will
drive the boat to 6 kts in smooth water (abso-fricken-lutely), it will always be true that having more hp will be better to maintain speed against a chop. Any engine around 18 to 23 hp will certainly do that.
All engines will have their limits of effectiveness-- that Catalina model has a lot
of fullness in the bow sections -- makes it real roomy inside but also is a "squarer" shape to force through a steep chop.
Back to basic speed, IF anyone tells you that their boat will not achieve 6 kts in smooth water, with a clean bottom, they Very Likely have a problem that is NOT related to their engine size.
So do not be afraid of owning an older Catalina with the smaller diesel. Spend your restless nights worrying about spongy decks, blown-out sails, and ancient standing rigging that's 15 years overdue for replacement.
Like all 'net opinions from total strangers, this on is worth about what you are paying, BTW.