The Proper Prop

SFS

.
Aug 18, 2015
2,066
Currently Boatless Okinawa
John, two different pieces of data. I interpreted Daveinet's question to mean "what answer do you get when you multiply the square root of waterline length by 1.35"? So I gave it to him. Clearly they exceeded hull speed, which you can do if you have enough thrust (horsepower).
 
  • Like
Likes: jssailem
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Remember talking to one of the engineer officer's on our trip home in 66. He said that the power in the boat was unbelievable. It might have been able to exceed Hull speed. At 16, hull speed calculations were a bit out of my normal activity. But I could look at the ship and hear the discussions of the crew. They knew what they were talking about. I was still thinking. This ship is sailing form South Hampton to New York. The same route as the Titanic... :yikes: my dad arranged a visit to the bridge with the Captain. Way cool for me. They have the ship on the east coast and are trying to rebuild parts of her as a historical site.
 
  • Like
Likes: jon hansen
Sep 20, 2014
1,320
Rob Legg RL24 Chain O'Lakes
Yes, hull speed and max speed may be unrelated. I was curious how close they were to hull speed and if they were exceeding it.
 
  • Like
Likes: jssailem
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Dave I think they were exceeding hull speed based on their power system.

For the time, I understand, that the hull design was innovative.

Here is a link to some of her propulsion data Specifications of SS UNITED STATES

Here LWL length was 940. Using the standard hull speed calculation you get 41.08 knots.

So the reported 43 knots is beyond the calculated "Hull speed".
 
Jun 8, 2004
10,024
-na -NA Anywhere USA
@jssailem and @Daveinet
At the age of 9 celebrating New Years Eve 12/31/59, my family was on the SS United States drinking Champagne to toast in the New Year 1960 to the theme song of the movie, South Pacific, supposedly sung by Italian actor Rosano Brazzi in our stateroom.

It was a rough ride I think from South Hampton to New York with a few small ice bergs sighted. The seas were rough. While swimming in the pool, the kiddy end was the deep end and the deep end was the kiddy end. I distinctly remember the ship rolling being thrown from the top bunk to the floor. Maybe I got my knot head Crazy or craziness from that.
I enjoyed being on deck with my dad wondering about the speed mentioning The titanic. We laughed very hard together as he was not only dad but my best buddy. A little over a year, I rode in a missing man helicopter formation with dad’s casket going to Arlington. Beside me with his arm around wrapped around my shoulder was Gus Grissom with verbal permission to ride on that helicopter from JFK. I CHERISHED that ride with my father on the SS United States ship
 
Dec 28, 2016
33
Hunter 34 MiddleR
My thanks to all you sailors who took the time to reply to my question about the proper prop for my Hunter 34. I really appreciate your valuable information. I think I'm going to try a 3-blade 15 X 11 prop on her and run the Yanmar at 2500- 3000 rpm's. You're right. I need to run her at higher rev's.
When I Winterized her, I went through the time end effort to drain all the coolant and re-fill . But now I learned that I used the wrong anti-freeze. You should not use regular automobile anti-freeze in a diesel engine. Something about automobile coolant not being able to dissipate the heat from the pistons and cylinder walls . Apparently, the diesel can be seriously damaged over time. So, I bought the proper stuff, and I have to re-do the job . I hate doing things twice !

The " Big U " is one of the greatest ships ever built; and definitely the fastest, bar some Naval vessels. It is a damned shame that she sits and deteriorates at a Philadelphia dock. Why is it that we can save and renovate a British liner - The Queen Mary, for stationary use, (and I'm glad about that) but we can't do the same for our own S.S. United States ? She's our county's ship !!! I was really hoping that she would be
re-purposed as a modern-day cruise/trans-Atlantic liner. But, I'm sure that she would be a popular and successful attraction in some
stationary, multi-purpose use. Why hasn't some well-heeled person or developer stepped-up to give her a new life ?
 
Dec 25, 2000
5,703
Hunter Passage 42 Shelter Bay, WA
Read an article several years ago about the super carrier class of steam turbine ships that we were part of; the Kitty Hawk. I remember her doing speed runs late at night while standing on the fantail in the North China sea. Sheesh. Reported speed to the public in those days was 32 knots. The article timed the super Constellation run from Hawaii to San Diego and calculated her speed at 55 knots. No idea how accurate the data, but no doubt about the speed.
 
Dec 28, 2016
33
Hunter 34 MiddleR
Since your boat is on the hard I would measure the prop's circumference then divide that number by 3.14 to arrive at the diameter. Both my 1987 Hunter 31 and 2004 Hunter 386 came with a two-bladed prop and could not achieve hull speed under motor. After replacing both with a three-bladed fixed prop I was able to achieve close to hull speed under motor. So its your call if you want more speed under motor. I find the three-bladed prop also provides better acceleration, which helps maneuverability, and maintains speed in choppy water. As Terry Cox suggested contact a prop shop for proper prop size and quote, depending on the type of prop (fixed, feathering, folding) you want and how much you want to spend.

For reference you can calculate the hull speed of your boat in knots as follows: square root of the waterline (not overall) length in feet multiplied by 1.34
Thanks very much for your reply. I'm going to to price a three-blade prop. If it's not outrageous, I think I'll give it a try. In particular, I think it will improve responsiveness, when I'm backing into my slip.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Might suggest you consider a CampbellSailor from WestbyNorth.
Kelsey is a wizard at helping a boat owner get the right prop for their boat.
 
  • Like
Likes: Mikem