CD Power Boat - Hull Speed

[C. Novack]

Does anyone know the hull speed of a CD 28 Open Sport Fisherman? Does anyone know the formula for calculating the hull speed? Can someone provide me with the name of the company (a contact name and tel number) that purchased the molds for the Sport Fisherman? All info and advice will be appreciated. I just repowered the boat with a Marine Power (Chevy block) V-8 and am looking for the info to ensure that I have the correct prop. The new engine produces 325 HP at the prop. The old Chrysler produced 275 HP at the crank shaft. Thanks for your help. Chris

[Art]

I Have a 28 flybridge with a Cummings 210 hp diesel. It had a gas engine. As far as the hull speed, it is a semi displacement hull. When on plane the more power you put to it the faster you can go. A full displacement hull has a hull speed because it cannot plane. If you want the most grab out of your prop you use the most pitch that will let the engine reach its rated rpm. If an engine is rated at 325 hp at 5,500rpm that means to put out 325hp the prop MUST let the engine rpm reach 5,500rpms. If it goes over that your prop is to small in pitch or diameter and could overrev the engine. When you have the perfect prop that lets you reach the perfect rpm then your boat has reached its fastest speed. The best way to acheave this on a new engine is with a veriable speed prop. This wowld be to expensive to do fo us so we rely on charts with known prop combos. I hope I have helped Art



kEARConner@aol.com

[marv]

Does anyone know the hull speed of a CD 28 Open Sport Fisherman? Does anyone know the formula for calculating the hull speed? Can someone provide me with the name of the company (a contact name and tel number) that purchased the molds for the Sport Fisherman? All info and advice will be appreciated. I just repowered the boat with a Marine Power (Chevy block) V-8 and am looking for the info to ensure that I have the correct prop. The new engine produces 325 HP at the prop. The old Chrysler produced 275 HP at the crank shaft. Thanks for your help. Chris

the speed is a function of the lwl of the boat the formula is related to the square root and 1.34. it can be found in most boat books.



mibrinn@aol.com

[Hobby Marine]

Chris:

The molds for the 28 are gone as I understand it. There is a formula to calculate what you are looking for. You need to know the following,
1. The wt of the boat
2. The old HP, shaft RPM and the size of the old prop.
3. The new HP and shaft RPM.
4. The size of the existing opening where the prop is, this will tell you the max. diameter of the prop. available.

I will send you the formula on Monday. I have the book at the office. You can send this information to most any Prop. MGF and they should be able to reccomend a prop as well.

Glen



glen@hobbymarine.com

[C. Novack]

Thanks to all for the information, I appreciate it. I guess that I will have to wait until I pull the boat for winter to get the information Glen said will be required to size the prop. I thought that I saw information on this site a while ago stating the location of the molds, perhaps that was for CD sail boat hulls.

Chris:

The molds for the 28 are gone as I understand it. There is a formula to calculate what you are looking for. You need to know the following,
1. The wt of the boat
2. The old HP, shaft RPM and the size of the old prop.
3. The new HP and shaft RPM.
4. The size of the existing opening where the prop is, this will tell you the max. diameter of the prop. available.

I will send you the formula on Monday. I have the book at the office. You can send this information to most any Prop. MGF and they should be able to reccomend a prop as well.

Glen

[Tom]

Chris, On an earlier post. Did you ever find the plumbing diagram for your water heater? I scanned that page in my manual and can send it to you via email if you still need/want it. Email me direct with your email address if insterested and I'll forward it to you. Tom

Does anyone know the hull speed of a CD 28 Open Sport Fisherman? Does anyone know the formula for calculating the hull speed? Can someone provide me with the name of the company (a contact name and tel number) that purchased the molds for the Sport Fisherman? All info and advice will be appreciated. I just repowered the boat with a Marine Power (Chevy block) V-8 and am looking for the info to ensure that I have the correct prop. The new engine produces 325 HP at the prop. The old Chrysler produced 275 HP at the crank shaft. Thanks for your help. Chris

TomCambria@mindspring.com

[John Walden]

Does anyone know the hull speed of a CD 28 Open Sport Fisherman? Does anyone know the formula for calculating the hull speed? Can someone provide me with the name of the company (a contact name and tel number) that purchased the molds for the Sport Fisherman? All info and advice will be appreciated. I just repowered the boat with a Marine Power (Chevy block) V-8 and am looking for the info to ensure that I have the correct prop. The new engine produces 325 HP at the prop. The old Chrysler produced 275 HP at the crank shaft. Thanks for your help. Chris

Check with Nauset Marine in MA or Robinhood Marine in ME for the Sport Fisherman hull .



jwalden@mediaone.net

[Edd]

Does anyone know the hull speed of a CD 28 Open Sport Fisherman? Does anyone know the formula for calculating the hull speed? Can someone provide me with the name of the company (a contact name and tel number) that purchased the molds for the Sport Fisherman? All info and advice will be appreciated. I just repowered the boat with a Marine Power (Chevy block) V-8 and am looking for the info to ensure that I have the correct prop. The new engine produces 325 HP at the prop. The old Chrysler produced 275 HP at the crank shaft. Thanks for your help. Chris

TRY http://www.boatplans-online.com/free/prop.zip

[Tom S.]

Does anyone know the hull speed of a CD 28 Open Sport Fisherman? Does anyone know the formula for calculating the hull speed? Can someone provide me with the name of the company (a contact name and tel number) that purchased the molds for the Sport Fisherman? All info and advice will be appreciated. I just repowered the boat with a Marine Power (Chevy block) V-8 and am looking for the info to ensure that I have the correct prop. The new engine produces 325 HP at the prop. The old Chrysler produced 275 HP at the crank shaft. Thanks for your help. Chris

Chris my 28 fly bridge with a 360 chrysler gas engine uses a 18X17 prop.A friend with the same engine with an open fisherman turns an 18X18 prop .This should give you a ball park.The correct prop pitch is the one that will give you the engine mfg.recommend top rpm .Tom



TShel11523@aol.com

[C. Novack]

Tom: Thanks for your offer regarding the diagram for the water heater. I have decided to hold off on the water heater until I pull the boat in the Fall. I have the CD Owners Manual. Thanks again for your information regarding the installation of the water heater, I appreciate it. Chris

Chris, On an earlier post. Did you ever find the plumbing diagram for your water heater? I scanned that page in my manual and can send it to you via email if you still need/want it. Email me direct with your email address if insterested and I'll forward it to you. Tom

Does anyone know the hull speed of a CD 28 Open Sport Fisherman? Does anyone know the formula for calculating the hull speed? Can someone provide me with the name of the company (a contact name and tel number) that purchased the molds for the Sport Fisherman? All info and advice will be appreciated. I just repowered the boat with a Marine Power (Chevy block) V-8 and am looking for the info to ensure that I have the correct prop. The new engine produces 325 HP at the prop. The old Chrysler produced 275 HP at the crank shaft. Thanks for your help. Chris

[Tom]

The plumbing diagram I have is from the Univesal Engine Service Manual. I'm not sure if the CD owner's manual has the diagram or not. You've probably alrady looked and know, but I've never seen one of the power boat manuals so I wasn't sure.

Tom: Thanks for your offer regarding the diagram for the water heater. I have decided to hold off on the water heater until I pull the boat in the Fall. I have the CD Owners Manual. Thanks again for your information regarding the installation of the water heater, I appreciate it. Chris

Chris, On an earlier post. Did you ever find the plumbing diagram for your water heater? I scanned that page in my manual and can send it to you via email if you still need/want it. Email me direct with your email address if insterested and I'll forward it to you. Tom

Does anyone know the hull speed of a CD 28 Open Sport Fisherman? Does anyone know the formula for calculating the hull speed? Can someone provide me with the name of the company (a contact name and tel number) that purchased the molds for the Sport Fisherman? All info and advice will be appreciated. I just repowered the boat with a Marine Power (Chevy block) V-8 and am looking for the info to ensure that I have the correct prop. The new engine produces 325 HP at the prop. The old Chrysler produced 275 HP at the crank shaft. Thanks for your help. Chris

TomCambria@mindspring.com

[Walt Bilofsky]

Does anyone know the hull speed of a CD 28 Open Sport Fisherman? Does anyone know the formula for calculating the hull speed?

Based on my experience with my CD 30 powerboat and not on any special knowledge -

There are basically three attitudes: hull down, on plane, and in between, a.k.a. "in the hole". I think if you graph speed on your knotmeter vs. RPM, and watch the boat's attitude, you will see pretty clearly where these ranges are. On my boat the speed increases smoothly with RPM until about 2000 RPM / 7.5 knots. Then the boat starts riding bow up and pushing lots of water as it tries to climb its bow wave. This persists until about 3000 RPM / 11 - 12 knots. At this point you start to see the waves from the aft corners of the hull crossing behind the boat in an X, and the boat is riding on the bow wave. From here on, small increases in RPM correspond to large increases in speed.

For best efficiency, I stay below 2000 RPM or above 3000.

All this applies to my 30, but it ought to be similar for your 28. The 28 is single engine and the 30 is double, also the 28 has a rounded bilge and the 30 has chines. But they are both semi-displacement and should work similarly.

- Walt Bilofsky



bilofsky@toolworks.com