distance from strut to prop?
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Boat Maintenance
Forum Discription: Discuss maintenance of your Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=13650
Printed Date: November-17-2024 at 4:32pm
Topic: distance from strut to prop?
Posted By: hotboat
Subject: distance from strut to prop?
Date Posted: May-12-2009 at 7:18pm
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2 yrs ago I shortened my shaft by 2 inches to get the prop within 1/4 inch of the strut, I was trying to get the 2 blade prop to run a little smoother. Just wondered if anyone knows the performance difference by moving the prop that much closer to the hull? ------------- Brian |
Replies:
Posted By: eric lavine
Date Posted: May-12-2009 at 7:51pm
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i would think you would since you moved it, thats not saying it sarcastically ------------- "the things you own will start to own you" |
Posted By: hotboat
Date Posted: May-12-2009 at 8:13pm
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Unfortunately I made a bunch of other changes at the same time,it did smooth it out some tho ------------- Brian |
Posted By: 8122pbrainard
Date Posted: May-12-2009 at 11:43pm
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Brian,
Hopefully before you cut the shaft off, you had the prop balanced/tuned, the shaft checked for straightness using a dial indicator, installed a new cutlass bearing and then lapped the prop onto the shaft. With a prop that close to the strut I'd be a little concerned about proper water flow through the cutlass. Can you still get a prop puller on it or do you need to separate the coupling halves? The prop should clear the hull by 10% of the prop diameter. I don't know the performance difference with running less than the 10% but I do know it hurts it. The turbulence created as the prop swings up towards the hull really creates a imbalance. With less than the proper clearance, you are also risking damage to the hull with prop burn. I've seen the gel gone and the glass hull eroded. BTW, the normal rule of thumb distance for the prop hub from the strut is 1 to 1&1/2 time the shaft diameter. ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: hotboat
Date Posted: May-13-2009 at 12:28am
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I was going on a recommendation from the prop manufacturer and it was only an 11 or 12 inch diameter so that prop wasn't as close to the hull but my acme is pretty close. Havent had any marks show on the hull yet and I can still fit the puller on. Maybe I will push he back out some though if I have enough spare still in there. My 90 Nautique was just as close to the strut but I dont recall how close to the hull the prop was? Thanks for the input! ------------- Brian |
Posted By: 8122pbrainard
Date Posted: May-13-2009 at 9:55am
"Prop burn" or "hull rash" isn't a mark but rather areas of errosion caused by water/air cavitation. So, how close is the new prop?
With your vibration problem, did you:
Your being a tool maker, you can certainly appreciate the importance of tight tolerances and concentricity's. ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
8122pbrainard wrote:Posted By: 79nautique
Date Posted: May-13-2009 at 5:27pm
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concentricity is not a very good means to control postion or orinentation and is not recommend to use it in todays world.
it's all most impossible to measure correctly since you have to find the actual centerline of the feature which will never be straight in the real world so it ends up being a derived best fit. Much cheaper and easier to control by using runout or true position with a cylindricity refinement if it needs tight control, but hey GD&T's not everyones bag and over 50% of the people that use it regularly are appling it incorrectly and measuring it incorrectly as well. yes it's in the ASME standards and Yes they used to make a gauge to check it but it's poor practice by todays design standards and it never is measured correctly. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: 79nautique
Date Posted: May-13-2009 at 5:31pm
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your a little close with the .25 gap it should be around 1/2 provided you have tip clearence as Pete stated, it does help it moving it closer to the strut, less flexx, changes the bow rise and does help the hole shot having it closer to the strut. It's not a huge difference but it is noticible. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: 8122pbrainard
Date Posted: May-13-2009 at 5:59pm
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Chris,
Thanks for bringing up the concentricity. I did use it as sort of a "catch all" term. "Run out" would have been better. ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: 79nautique
Date Posted: May-13-2009 at 6:11pm
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when you look at it that is what you are trying to control, the center of this is the center of that, and it was pretty common practice, but as more and more learn the proper applications of GD&T the standards committy started backing off endorsing it's use and several company's do not allow for it to be use and state so in their own standards manuals. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: hotboat
Date Posted: May-14-2009 at 1:18am
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wow thats alot of words? the 2 blade was the closest to the the strut and at min it was qrtr in. the acme sits back a little further maybe 3/8 or a lil more. The ideas of the v-drive props was more boat out of the water to start with and from the pics u show me of burn marks, I have none. Maybe you guys could come play with my boat for fun? ------------- Brian |
Posted By: TRBenj
Date Posted: May-14-2009 at 11:31am
Bring it out to CT and Ill wring it out for you! ------------- |
Posted By: hotboat
Date Posted: May-14-2009 at 7:09pm
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Where is CT? ------------- Brian |
Posted By: TRBenj
Date Posted: May-14-2009 at 7:15pm
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Right near Connecticut. ------------- |
Posted By: C-Bass
Date Posted: May-14-2009 at 7:26pm
^^^  Haha, yeah very near.------------- Craig 67 SN 73 SN http://www.correctcraftfan.com/diaries/details.asp?ID=6103" rel="nofollow - 99 Sport 85SN |
Posted By: 8122pbrainard
Date Posted: May-14-2009 at 11:10pm
Brian, This is a map of the United States of America. If you look in the upper right corner of the country, you'll see Hartford CT. shown. CT. is the abbreviation for Connecticut. 
Also, here's a list of the states abbreviations if it will help. State/Possession Abbreviation ALABAMA AL ALASKA AK AMERICAN SAMOA AS ARIZONA AZ ARKANSAS AR CALIFORNIA CA COLORADO CO CONNECTICUT CT DELAWARE DE DISTRICT OF COLUMBIA DC FEDERATED STATES OF MICRONESIA FM FLORIDA FL GEORGIA GA GUAM GU HAWAII HI IDAHO ID ILLINOIS IL INDIANA IN IOWA IA KANSAS KS KENTUCKY KY LOUISIANA LA MAINE ME MARSHALL ISLANDS MH MARYLAND MD MASSACHUSETTS MA MICHIGAN MI MINNESOTA MN MISSISSIPPI MS MISSOURI MO MONTANA MT NEBRASKA NE NEVADA NV NEW HAMPSHIRE NH NEW JERSEY NJ NEW MEXICO NM NEW YORK NY NORTH CAROLINA NC NORTH DAKOTA ND NORTHERN MARIANA ISLANDS MP OHIO OH OKLAHOMA OK OREGON OR PALAU PW PENNSYLVANIA PA PUERTO RICO PR RHODE ISLAND RI SOUTH CAROLINA SC SOUTH DAKOTA SD TENNESSEE TN TEXAS TX UTAH UT VERMONT VT VIRGIN ISLANDS VI VIRGINIA VA WASHINGTON WA WEST VIRGINIA WV WISCONSIN WI WYOMING WY ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: SUNAPEE CROW
Date Posted: May-15-2009 at 1:29am
| CONNECTICUT...... The place where the DUMBEST MOST AGGRESSIVE DRIVERS live and work. I hate I 84!! Try Hartford at 3:30 on a Friday going either East or West. It is far worse than metro Boston and we have the illegals that can't read!! English that is. |
Posted By: hotboat
Date Posted: May-15-2009 at 4:55am
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I went to Boston once to meet the hottest chic, I had to fly to 3 dif cities first and met 3 more on the way...so this is sounding like a good idea...I have to leave for a wsop game but will return in a week...sorry bout the vacation? ------------- Brian |
Posted By: TRBenj
Date Posted: May-15-2009 at 2:09pm
Rick, I do the metro Boston commute every weekday, and I still get to enjoy the Hartford traffic on Friday afternoons. Its the best of both worlds, really.
Brian, the offer still stands to give that Mustang a good shakedown! ------------- |
Posted By: C-Bass
Date Posted: May-15-2009 at 6:41pm
I don't know about Boston, but when I was interning for Pratt&Whitney I had to commute down I-91 to I-84 East in Hartford to East Hartford...definitely more traffic than I was ever used to growing up in the mid-west. The shear volume is bad yes, but the drivers aren't any dumber than anywhere else in the country. Stupid = the real pandemic ------------- Craig 67 SN 73 SN http://www.correctcraftfan.com/diaries/details.asp?ID=6103" rel="nofollow - 99 Sport 85SN |