What's my pitch?

[iggyw1]

I have a 1991 70 H.P. Nissan motor. I removed my prop in hopes of getting it repaired during the winter months, it has some slight damage to the blades. The only markings at all that I see on my prop is the number 12 that is embedded right into the side of the prop. Would this be the pitch of the prop or the diameter of it? There are no other numbers or letters anywhere on the prop, inside or outside. If this 12 indicates the diameter, how can I figure out the pitch? I assume a prop shop can figure that out when I take it in for repairs,, correct? I am thinking they can tell me both, the diameter & pitch of the prop that I have, but I am not sure, Thanks!

[pvanv]

So you have either an NS70A2 or an NS70B. Year is irrelevant on these.
Yes, the 12 is the pitch.

[iggyw1]

So you have either an NS70A2 or an NS70B. Year is irrelevant on these.
Yes, the 12 is the pitch.

Yes, I have an NS70A2. I meant to include this in my post but I failed to. Can the repair shop figure out my pitch from my prop I am taking in for repair? How much bigger on the diameter can I go? We have no Nissan dealers around me anywhere, but I tink any place else (Evinrude/Johnson prop shop) should be able to repair my prop, correct or do they just stick to their own brand usually?

[pvanv]

Changing diameter on an OB prop has minimal effect. You have a nominal 12 pitch now.
You can see the OEM props available at https://tohatsu.com/accessories/prop.html
Typically any prop shop can repair damaged blades. If you need a re-hub, consider a new prop, and keep the old one as a spare.

[iggyw1]

Thank you very much for your help. I appreciate it. Fortunately, the hub looks great. The blades are not really too bad at all, but they can use a repair to make them like new. I will also get a new one if I can find out the pitch that I have. I do not want to change the pitch as I am very happy with the performance of the prop that I have.

[Sea Rider]

Diameter is all about what the prop manufacturer wants to play width, pitch is all. If that's the original prop the motor came with, how do you know that performs top. You should change the factory delivered prop which is usually a medium pitch to at least one lower one to increase a bit the wot rpm range towards middle to max of its wot rpm range which is 5500 to 5800 rpm. For that will need a tach, does the motor has one ? Running any motor with an optimized prop as usually loaded it's a day/night boating difference..

In reality the motor needs to work inside it's factory wot rpm range, running happy is no indication whatsoever at which wot rpm the motor is working as usually loaded.

Happy Boating

[iggyw1]

I am running at 5600 RPMs at WOT, and I am doing 34 MPH with me & my cousin in the boat (we both weigh 380 pounds each), so I am happy. I have a 16' 7" alluminum Smoker Craft. I do not know if the prop I have is original or not, but I do not want to go over 5600 RPMs so that's why I am happy with my prop. The book that I have states the RPMs should be 5500 to 5600. IEven if I can go to 5800 RPMs and I only gain (1) MPH, is it worth running the motor at 5800, the very max.? Isn't that pretty hard on the motor for one MPH, or am I thinking wrong on this point? Thanks.

[pvanv]

Your WOT is OK. anything around 5500 is the sweet spot.

[iggyw1]

Your WOT is OK. anything around 5500 is the sweet spot.

Thanks Paul. I still have to get my prop into a shop. No hurry here in Michigan until sometime in mid to late February actually. Cannot get on the Detroit River until the end of March to early April for the walleyes. Late April on Lake St. Clair.

[Sea Rider]

Right on, 5600 wot revs corresponds to the older models, 5800 wot revs corresponds to the newer 70 D model. You're there nothing to improve already running at max wot as loaded which is excellent at whicherver throttle setting you like. If plan going for a new prop install same as previous..just check diam and pitch.

Happy Boating

[iggyw1]

I got my prop back from the shop and it looks like a brand new prop. Cannot wait until the ice leaves tha lake in late March to get out onto the water in my boat. Still could not find out what pitch I have. The prop mechanic did not know how to tell. The only numbers embedded into the prop are a 12 with a circle around it on the side of the prop, and inside the prop it states D-5. The diameter is 12". What does the D-5 mean? Anyone know? Thanks.

[pvanv]

D5 could refer to the cavity used when it was cast. The 12 is what you need.

[iggyw1]

Thanks once again Paul. You said the 12 is what I need. I know what the diameter of the prop is because I measured from the end of one of the three blades to the center of the prop shaft hole then multiplied X 2. My prop is a 12" diameter prop. Is the 12 on the side of the prop indicating a 12" diameter or is the 12 on the side of the prop indicating a 12 pitch? I am after finding out what pitch this prop is because it works fine for me and I want to get a duplicate of it as a spare. If the 12 on the side of the prop is not the pitch, how can I measure what pitch it is?? Sorry to be such a pain about this, but I really would like to find out what pitch my current prop is, and nobody is telling me definantely that the 12 is the diameter or the pitch. Which is it?

[pvanv]

The prop shop should be able to tell you. But, since pitch is the only number of interest on these, you should have 12 pitch.

From the Tohatsu prop table (available online at Tohatsu.com):

ALUMINUM	MODERATE	11.5	13	3		353B641050	2-CYLINDER MODEL
ALUMINUM	MODERATE	11.6	12	3		353B641040	2-CYLINDER MODEL
ALUMINUM	LIGHT	10.9	17.6	3		353641090M	2-CYLINDER MODEL

So the current props are 13, 12, and 17.6 pitch. You must have a 12.

[iggyw1]

Thank you very much. I will order a 12 pitch propeller and go with that. I am just going to get an aluminum prop like I already have. My boat planes real good, my RPMs are running at 5600 and I am getting 34 MPH with two big guys in the boat. It's a 70 H.P. Nissan and a 16' 7" aluminum Smoker Craft boat. I'm happy with it's performance all the way around. All I need now is for the ice to leave our lake LOL (ice did not even appear yet, but boat has been winterized here in Mich.) Thanks!