Propeller for Mainship 34

[Jacques Raoul]

I hit bottom and badly damaged the prop and shaft. I have a spare shaft and it was changed. Now the prop, here is the question. This prop is 4 blades, 19.5 dia. and 23 inches pitch. With this one the perkins (210hp) turns at its 2500 rev. The spare prop on it now is 19.5 dia. and 26 pitch. I did not rev too much the perkins and at 1600 rpm got a small vibration, but surfing on following seas, vibration stop. I think vibration may be cause by cavitation?
Where can I get the prop fix or a new one made?

 

[Nomad Willy]

The pitch/diameter ratio seems way off. A 19” dia should have a pitch of about 15”. And prop overloading is very likely and hence cavitation. And surfing would relieve some load and reduce or stop cavitation.
Sounds like you need more prop dia. How much prop tip clearance is there?

 

[DavidM]

Ask around at your marina or local boat yards for a recommendation for a good prop shop. A prop shop can usually adjust the pitch up or down a few inches. They will also true it up.

David

 

[Jeff F]

I have a sistership, and have a 20x24. It's about right for 210 hp with a 2.1 reduction gear. You can't go bigger in diameter. I suspect you might be overpropped with the spare.

There should be a prop shop serving your area. Ask around. They should be able to help.

 

[jleonard]

Actually the 79 and newer ones can go a little larger as they have a greater shaft angle and a dropped down skeg.
You could probably go 21 x 21 and be pretty close.

 

[Jacques Raoul]

Many thanks to you all

The 19.5 by 23 did not vibrate even at 2500 RPM, the design RPM for the Perkins. Is it possible that the cutlass bearing being damage?

 

[DavidM]

It is possible but not likely the cutlass bearing was damaged. Easy enough to check either with a haul out or with a dive. Grab the prop and wiggle it up or down side to side. Should not move more than 1/32"-1/16"

More likely the 26" pitch prop is out of true. A quick test but not definitive is to hold a fixed point very near one of the blades and rotate it and see if the clearance stays +/- 1/8". Not easy to do underwater though but a diving service may have the skills.

David

 

[Solly]

Was the spare shaft checked for true b-4 installing ? Is it brand new or maybe one taken off sometime. Do you have the intermediate bearing and checked ?

All I'm saying is 2 things changed so it could be either.

Think I read somewhere a prop shop can change the pitch around 1 inch. Have to find a shop.

 

[Chris Kate]

Mainship 34 Greece

Hauled out yesterday and noticed the prop has a few chips on one of the blades. I will recondition it however, I would like to keep it as a spare and purchase a new prop. Is there a stock prop option? The motor is 1981 Perkins 3544 Turbo rated at 180 HP. Currently getting up to 2300 rpm. I cruise at 1700 rpm and get 9.5 knots on a calm sea with 17.5 liters per hour. . Top end speed is 13.6 on clam sea. Thank you all for your input.

 

[Chris Kate]

https://photos.app.goo.gl/SmZbGCNB27xMsDfN7

 

[Grupet]

In the picture, there appears to be a lot of overhang, distance between the cutlass and the prop? Could just be the picture, but you might want to measure and ask your prop shop.

 

[Chris Kate]

Hello Groupet,

The amount of visible shaft is what you are referring to? I do not know about any specific requirements for this overhang. Do you? Thank you for your reply.

 

[Grupet]

I replaced the shaft in my 34 Mainship mk3 with 200 Perkins a number of years ago. I believe the prop shop said no more than 1.5x shaft diameter?

There was only space for a donut style zinc on the shaft. I dont know what your distance is, or if it would cause the issues you're asking about.

Just wanted to mention it looks different than mine did, and you may want to check into it.

 

[Jacques Raoul]

My prop is a 20x22, four blades. The engine is a Perkin 215hp and the gear box is a Velvet 1.91/1.00. This prop was purchase a year ago and used as a spare. This summer I put it on and could feel it vibrate at 2000rpm and higher. At the winter haulout, we removed the prop and sent it for being balanced!!! Outch. The manufacture inspection sheet says it was balanced!!!

 

[Gdavid]

Most of the old 34' Mainships have 1 3/8" prop shafts, I believe the 1977 models had 1 1/2" bronze shafts but the rest had 1 3/8" stainless steel shafts. My 1980 with a 165 hp T6.354 Perkins has a 20x20 prop, my transmission is roughly 2/1. At 1700-1800 rpm I am only doing about 7.5 knts so your prop must have significantly more pitch than mine. I believe they all had transmissions around 1.9-2/1 reductions, so I doubt yours would be much different.

 

[Chris Kate]

Hello gDavid, thanks for your reply. I have to check on which transmission I have. At idle , I'm doing 5 knots in flat water, and the fuel usage at idle is quite high 6 liters ph! I measured the fuel consumption by using a gerry can, a white plastic diesel container that I had premarked at 1-liter intervals! So I'm sure about my consumption. And at 1700 rpm I was doing 16 liters per hour at 9.5 knots flat water. I am very happy with the propeller and just want to make sure I get the same one, as I use the boat as transportation 6 months of the year, I live on a small island and need to shop for everything off the island, 1 hour each way, in open sea conditions. Past 6 months I put 135 hours on the engine.