Increase speed

[alfin32]

I've got a '87 CD Open Fisherman, Hull #109, that I love.
It cruises at about 12 kts with a 275hp Chrysler Gas V-8.
Is there any way to increase the speed to a high teens
cruise or am I limited by the shape of the hull? Any
suggestions would be appreciated.

[Paul D.]

Though I am a die hard sailor and have limited knowledge of powerboat workings. I did once work in a marina and at that time read a wonderful book with good, understandable information on your question. I recommend The Nature of Boats by Dave Gerr. There are several chapters in there that discuss the relationship between hull shape, horsepower, speed and displacement.

I bet you would find it helpful in getting the most speed out of your boat.

All the best,
Paul

[bill2]

FWIW

The formula for max speed for a displacement hull is easy:

1.34 X the Square Root of the Boat's Waterline Length
(This is Theoretical Maximum Hull Speed)



Now if you ( your hull ) can get up on plane then . . .

- usually ends up being about the money being the limit

[Cathy Monaghan]

CLICK HERE to view the specifications for the CD28 poweryachts.

I am no expert, so take all this with a grain of salt.

According to the specs, the Open Fisherman should cruise at 14 kts, top speed somewhere around 20 kts.

According to the owners manual, the 280 Sport is the lightest model at 6500 lbs, followed by the heavier Open Fisherman at 7000 lbs, then the Cruiser at 8000 lbs, followed by the Flybridge Cruiser at 8500 lbs.

The lightest boat (280 Sport) should cruise slightly faster than the Open Fisherman and the to Cruisers will be slower.

Has your boat been re-propped? The wrong, or incorrectly pitched, prop could be the culprit if she's not performing properly. But 12 kts isn't far off the mark for the Open Fisherman.

Hope this helps,
Cathy
CD32 Realization, #3

[Steve Laume]

Somehow a Star Trek dialog comes to mind here. We need more speed Scottie...

A clean bottom, the right prop. Or a lot more money might get a wee bit more speed.

I am always happy if I can cruise at 5 knots, Steve.

[alfin32]

Thank you for all the input.
I'm going to check the prop,
but just wanted to make sure
there wasn't some known
upgrade I wasn't aware of.
I'll keep you posted on my
findings.

[Chris Reinke]

As a former non-CD power boater I can not offer any specifics to your model but rather a bit of information from my experiences. I found on my old 25' is that hull trim is a much easier issue to address then power upgrades, or prop replacement. Have you evaluated your trim or do you have trim tabs on your Open Fisherman? How does she ride it cruising speed? On my boat I found the bow to ride low, thus plowing into the waves and reducing hull performance. I did not have tabs so I would empty my bow tank and relocate my anchor and rode to an aft compartment. The result was an increase of 2-3 knots at cruising RPM's.

[Bill - Dulcie]

The CD 28 hull speed is about 20kts. Much over that, she'll "keel-walk" and become unmanageable. That said, my Dulinea, a 28 flybrige cruiser with a 200hp Volvo diesel, would do about 18-19kts with a clean bottom and light load, UNTIL I hit a sinken container of the Chesapeake and broke off a prop blade. The replacement prop was the wrong size/cup. WOT with the new prop was 13-14kts. Re-pitched it. Got 15. Re-pitched again, got 15.5kts. Finally took her to good prop-shop. They replaced prop again, she'll now do about 18.5kts WOT, close to her new performance. With a 275hp engine in a lighter boat, you should be getting at least 18kts WOT, perhaps more. Assuming the engine still delivers at/near rated power, it's the prop, sir, it's the prop.

Manufacture's specs for engine should tell you WOT rpm rating. If she turns significantly short of that number at WOT, again, it's the prop!

[alfin32]

We've got a great prop shop in Salem, Ma.
I'll take it over there this week.
Thanks for the advice.