C28 Prop size

[Rob Hindman]

I would like to verify that my C-28 has the correct prop. I believe we have corrected an overheating problem, but still can't get much more than 1200rpm's out of the MD7A without running the temp up. The previous owner added a 3 blade. I'm going to attempt to pull it off next week and verify the size. Any thoughts would be helpful. As always, thanks for the great advice!



robhindman@earthlink.net

[Ken Cave]

Measuring a prop is more an art than a science-you gotta take the weight, the size of boat (and all the goodies that go with it) the engine horses, and put them all together to make a package! Now, this will come with pitch, blades, size of blades, etc. etc. etc.

Sounds like you got a prop that is way too aggressive for your 13 horses! I installed a three bladed prop on my MD7A which had the rpm's of my old two bladed prop-but did an average of 5.5 knots!

What you need is a good prop shop!!

Ken Cave
CD 28 # 227
Anacortes, WA



bcave@whidbey.net

[Don Frazier]

Rob,

28 came with a 2 blade 13x13 left hand prop.
Ken, what size is your 3 blade?

Don
CD 28 #152
Waldoboro, ME

Measuring a prop is more an art than a science-you gotta take the weight, the size of boat (and all the goodies that go with it) the engine horses, and put them all together to make a package! Now, this will come with pitch, blades, size of blades, etc. etc. etc.

Sounds like you got a prop that is way too aggressive for your 13 horses! I installed a three bladed prop on my MD7A which had the rpm's of my old two bladed prop-but did an average of 5.5 knots!

What you need is a good prop shop!!

Ken Cave
CD 28 # 227
Anacortes, WA

frazierauto@msn.com

[Jerry Hammernik]

Ken,
Can you share with us the specifics of your 3 blade. And did you notice a difference under sail, and if so, how much?

Jerry Hammernik
Lion's Paw CD28 #341
SSYC, Milwaukee, Lake Michigan
On a scale of 1-10, last Sunday's sail was a 12

Measuring a prop is more an art than a science-you gotta take the weight, the size of boat (and all the goodies that go with it) the engine horses, and put them all together to make a package! Now, this will come with pitch, blades, size of blades, etc. etc. etc.

Sounds like you got a prop that is way too aggressive for your 13 horses! I installed a three bladed prop on my MD7A which had the rpm's of my old two bladed prop-but did an average of 5.5 knots!

What you need is a good prop shop!!

Ken Cave
CD 28 # 227
Anacortes, WA

dauntles@execpc.com

[Joe Sankey]

Bob, I can't be much help, but I think Ken's advice about a prop shop is good advice. I had an experience when we bought our (former) CD28 that is nothing more than a cautionary annecdote: At survey the engine would not turn up under power to the satisfaction of the surveyor; too much differential in the unloaded/loaded RPMs. The survey was done in Lauderdale; boat was shipped to Pensacola where I had bottom work, etc. done. While on the hard I inquired with the (then) two major prop manufacturers; both had on-line inquiry pages to size props. I got two very different answers, neither of which was what was on the boat, which was a 3 blade. I threw up my hands, left it alone, and never had a problem. My point is that even the experts disagree, or at least have very different criteria for solving the problem. By the way, if your Volvo is fresh water cooled, check your hoses for inside delamination from the wire. I've had one act as a check valve at higher RPM when it would close, causing overheating of a Universal M18.
Good Luck
Joe Sankey
CD 30 Slow Dance

I would like to verify that my C-28 has the correct prop. I believe we have corrected an overheating problem, but still can't get much more than 1200rpm's out of the MD7A without running the temp up. The previous owner added a 3 blade. I'm going to attempt to pull it off next week and verify the size. Any thoughts would be helpful. As always, thanks for the great advice!

sankey@gulftel.com

[BenThomas]

I would like to verify that my C-28 has the correct prop. I believe we have corrected an overheating problem, but still can't get much more than 1200rpm's out of the MD7A without running the temp up. The previous owner added a 3 blade. I'm going to attempt to pull it off next week and verify the size. Any thoughts would be helpful. As always, thanks for the great advice!

Rob, Before I repowered with the beta-marine 722 (20hp) on my cd30 I had the volvo MD7A. I had the same low rpm problems at one time although the engine never overheated. The throttle linkage was not adjusted properly and was fouling on brackets by injector pump. You might check linkage and make sure its lubricated and runs true and fair. This done on my engine picked up a couple hundred rpms. My prop was a two blade 13x13. I switched that out to a three blade 13x8. left hand (machine pitch) much more thrust, engine cruised at 1800 to 2000 rpms at 5.6 knots. I may have lost speed under sail, but nothing that was substantially noticable. The trade off was more punch through the crud under power.
I am now running a 13x9 right hand three blade with the beta. I have the 13x8 three blade still, one year usage in the box and its for sale. I also have a two blade 14x8 which worked with the volvo. thats for sale as well. I have four new injectors for the volvo MD7A. Serial number: Bosch #043 KBAL65P9/4861. I will accept any reasonable offer for any or all of these items.
Higher rpms means the cooling system has to be working well with no obstructions in intakes, strainers, piping and the impellor intact doing its job and the thermostat working properly, maximum flow through the system is essential. you might want to check those items.
Is the engine under load at only 1200 rpms or is it in neutral (no Load)?



bt@benthomaslandscapers.com

[Tim Akers]

Rob, it sounds like you are in the same place that I was a year ago. My 1976 md2b raw water engine on my CD28 ran hot ever since I bought it in 1996. The left hand engine came with a 13x13 2 blade prop. I varified with Volvo, that the design perameters required this prop. I tried everything that I could think of including an acid flush of the cooling sytem, new temp. senders, guages, pumps, lines. It drove me nuts. There was no sea strainer on her when Purchased. I immediately installed one. I eventually concluded that the engine must have ingested something and that there was not much that I could do. None the less, I put 500 hrs. on her while nursing her along at usually around 1800rpm.

In January The Vovlo swallowed a valve not too far from my dock. With the help of a strong davit, good freind, and a few cold beers, I now have a Yanmar 2qmf (freshwater cooled) engine with 50 hours on it. It was a pretty simple refit and I have peace of mind.

I know this is not quite the news you were looking for but I hope it is food for thought. I sail her out of Ft. Lauderdale around the Bahamas, Keys and Cuba with my family. Yanmar engines are universally available, and dependable. If you get to this stage in your problem solving process drop me a line and I will be happy to share any info. that I can.

Good Luck,

Tim Akers
Night Wind CD28 #67

I would like to verify that my C-28 has the correct prop. I believe we have corrected an overheating problem, but still can't get much more than 1200rpm's out of the MD7A without running the temp up. The previous owner added a 3 blade. I'm going to attempt to pull it off next week and verify the size. Any thoughts would be helpful. As always, thanks for the great advice!

fullboat6@yahoo.com

[Ken Cave]

As I have installed a new 2020 Volvo (actually Perkins painted green) the company that installed it put in a right hand 13x08 which I think means that it is a 13 inch prop with a an 08 pitch. My 2020 can actually run at 3600 rpm but I like running it at around 2900 rpm, which gives me a quiet ride at 5 honest knots. I really do not believe that this prop hurts the sailing aspect as much as the 7ft. Quicksilver I tow just about everywhere (this year-over a thousand miles!!)

Unfortunately, we usually motor 80% of the time, and sail 20% as summer winds in the northwest are usually nill to none-or right on the nose!

Next time I pull my boat, I am thinking of re-pitching the prop to make it a little more aggressive. As the engine winds up to speed without any hint of problems, it should be no problem.

Hope this helps

Ken Cave
Just back from 5 days of motoring in the northwest!
(but the weather was out of this world!!)



bcave@whidbey.net