45 hp prop question

[conor1366]

I have a prop that has 11.5 stamped on it and I took a compass to it and it measures about 10.5" diameter. The 11.5 is the pitch

this came off a 1975 45 hp. The center insert looks a little crooked...not off center but not level with the back of the flat part of the prop.

On the lake my 15 ft v-hull bayliner trophy bass did not plane up or go over 15 mph. I has less than 350 lbs total worth of people in it.

Could this have something to do with it?

I searched the forums for info but can't get a straight answer.

I am looking for a recomendation for a prop that will get me joyriding faster than 15 mph and not costing 300 bucks.

 

[roscoe]

Re: 45 hp prop question

At this point, we do not know if the prop is the problem.
More important right now is to determine the WOT rpm's, the compression readings, and if you are getting strong spark on all plugs.

It could be that the prop has spun its rubber hub.

The best place for props for your Chrysler motor is Propcopropellers dot com.

Of course iboats also sells them in the mall.

 

[Frank Acampora]

Re: 45 hp prop question

It is actually 10 3/8 diameter by 11.5 pitch. It is probably the correct prop. My 55 on a 15 foot runabout used a 13.5 pitch prop and gave me 27 MPH with only myself in the boat and 2 tanks of gas.

If it is the stock prop, (thick aluminum blades with rounded ends and blades appear to be bent back) this was made by a company called Columbian. These props were a bit "sloppier" and the blades were thicker than a Michigan. The hubs usually were a LITTLE off center. The operative word is LITTLE.

However, they still gave adequate performance

Check to see that the hub is not slipping. Do this by removing the prop and marking the center hub and the center of the prop casting. Run the engine on the boat, in the water. If the marks have moved relative to each other, the prop has a spun hub and needs either to be re-hubbed or replaced. With the price of re-hubbing it would make sense to buy a good used prop.

If the prop is not slipping, then you need to check the engine--everything from points to fuel delivery. AND, don't forget to check the engine tilt. Usually the best setting is the 3rd hole out from the transom. In too far and the boat will ride bow down and loose speed. Out too far and it will ride bow high and possibly not get on plane. Most smaller boats plane somewhere around 18 MPH so you may just not be getting it out of the hole

However, with that engine and boat, if you get it to 25, you are doing very well. 22 would more likely be an acceptable top speed.

 

[conor1366]

Re: 45 hp prop question

I was riding it on the closest setting to the transom and it was bow up.

would changeing the depth in the water help? right now it is sitting pretty low below the bottom of the boat...I would say 10-15" deeper than the boat bottom.

I am going to order the gaskets and diapragm for the fuel pump and rebuilt it.

the compression is 118 in #1 and 125 in #2

I'm not sure how to chech the points....

I read a thread that said I need a tach as well.

 

[conor1366]

Re: 45 hp prop question

it looks like the origional prop....its a beast. thick blades...looks like it came off a WW11 PT boat.

can you recommend a safe pitch and diameter prop that won't beat up the motor?

 

[eurolarva]

Re: 45 hp prop question

By no means a prop pro here but the standard prop that came with that motor is a 287 prop which would be 10 3/8 x 11 1/2. I want to think you are going to get max speed out of this prop. The next one in line is 293 prop which is 10 1/2 x 12. I posted these in the prop section and never got an answer to what effect will there be switching to the 293 prop. Use the words Roscoe put in his post. Those props are around 70 bucks. I tried to snipe one on ebay a couple of weeks ago but my virus program started doing an update and I could not send the bid in time. Prop would have been 45 plus 10 for shipping.

 

[conor1366]

Re: 45 hp prop question

Thanks eurolarva. I checked out the site that Rosco said and the props are 73 bucks...not bad. Better than Michigan for $123.

I will try the 10.5 x 12 and see how it goes.

 

[Frank Acampora]

Re: 45 hp prop question

The correct setting for the engine is that cavitation plate should be even to slightly higher than the point of the VEE in the bottom. Too far down and there will be too much drag.

It sounds like even with the engine tilted all the way in, the boat will not get out of the hole and on plane. It is a vicious cycle because with an engine that small, and the bow high attitude, the engine is sitting deep and can not develop enough of its horsepower to get the hull over the hump and on plane. So, it just wallows along like a garbage scow, making you think there is something wrong with the engine. Try moving some weight--any weight you can-- forward and see if it helps. Try taking one or two people and have them sit forward until the boat planes. This is one case where you may need to try a whale tail or trim tabs. Whale tail is cheaper but trim tabs are better--so see if a hydrofoil is any help first, then possibly buy trim tabs. Lots of the guys on iboats swear by Smart Tabs--think they are the best thing since sliced bread.

 

[roscoe]

Re: 45 hp prop question

Bottom red line is the bottom of the hull.

Anti ventilation plate should be just above.

 

[conor1366]

Re: 45 hp prop question

Cool...I get it now. I am thinking I may invest in some fins for the cavitation plate and that may help.

Next time I go out I am going solo and am putting some weight in the front to help it out of the hole.

I am doing the fuel pump tonight and hope to be on the water next week after my rebuilt lower unit comes in from MO.

The pinion gear was ground down quite a bit when I disassembled it...could that have been a root problem as well?

 

[conor1366]

Re: 45 hp prop question

so I have established that the prop that I have with my 45 hp chrysler is the origional, big, nasty, heavy, black, thick, PT boat style prop. If I got the same pitch and size, just different material (stainless steel), would it help out the power?

of course this is all hinging around RPMs that I need to check....and the tach I still have to buy and install.

 

[eurolarva]

Re: 45 hp prop question

I doubt you will find a stainless steel prop for that motor. My 45 will do about 28 mph on a 16 ft aluminum bluefin with me in it. I am guessing the only prop available is going to be an aluminum one.

 

[conor1366]

Re: 45 hp prop question

is it worth getting mine re-hubbed?

 

[eurolarva]

Re: 45 hp prop question

If there are no dings and the place you take it to is reputable go for it. Hard to beat a new one for 70 bucks though. Then again there is shipping.

 

[conor1366]

Re: 45 hp prop question

shipping is no more than 10 bucks...if that. I ma just do that.