Advice on prop size for 40HP Mercury on 17HP Lowe Roughneck

[netsomnia]

Motor: 40 HP Model Mercury ELTPO
Prop: Unknown but worked good until I bent it
Boat: 17 foot Lowe Roughneck all aluminum - no wood

Questions: Anyone experienced with matching prop on this boat? What is a mid-range prop size for this boat and motor? Mid-range meaning the middle of the pack for hole shot and WOT RPM and MPH.

I have no idea what the old one was and I want good hole shots while not sacrificing too much top speed. Of course, I could examine the older one and match up that way but if someone has experience with this setup I want to hear from you.

Thank you.

 

[steelespike]

Re: Advice on prop size for 40HP Mercury on 17HP Lowe Roughneck

Please read the stickies at the top of the page.Unless someone happens to have the exact setup prop selection will be a crap shoot.
A prop shop may be able to repair your prop.
Your old prop should have numbers on the barrel or under the prop nut.
If your going to fiddle with a prop you should have a tach and gps or speedo.
Depending on the present prop; now is the time to upgrade. Check out the turning point props.

 

[hwsiii]

Re: Advice on prop size for 40HP Mercury on 17HP Lowe Roughneck

Netsomnia, we will try to help you as much as we can, but there is certain information that is needed in order to help you. The following form has all of the information that is needed to help you with your problems finding the right prop. If you do not know all of the information that is asked for on the form please give us the most information you have available as I have a program I designed to find the right prop for any planning hull boat that needs this information, and anyone else who is trying to help you will need the same information. It requires time to find all this information when we have to look for it and in my defense I expect you to be willing to expend as much effort in finding the right prop as I do. We hope to be able to help you get the exact prop you need for your particular uses, and this information is required to do that.
It is not as simple to pick the right prop as most people coming to this forum think it is, that is why we ask so many questions, it is for your benefit we ask all these questions. And if you have a stainless steel prop or are changing to one the blade geometry of the prop can make a lot of difference in speed and RPM.

Iboats Boat and Motor Info

1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make and model of motor
7. HP and gear ratio of motor
8. Manufacturer?s recommended WOT range
9. Antiventilation Plate height above keel of boat if it is an outboard in inches
10. Make, model, diameter, pitch and whether SS or aluminum prop
11. WOT RPM and speed from each prop

H

 

[netsomnia]

Re: Advice on prop size for 40HP Mercury on 17HP Lowe Roughneck

Thanks for the detailed inquiries about my boat. Here is my detailed response - I do not completely understand question 11 - please elaborate:

1. Year, make and model of boat - 1993 OMC Aluminum Boat Group, Lowe Roughneck 170AW
2. Length, width and base weight of boat, look for boat decal on back of boat - 17ft, 6'1", 675#
3. Number of people and gallons of gas normally on boat - 4 people, 12 gallons
4. What do you use the boat for - Fishing in lakes and rivers
5. Is it a Deep Vee and if so how many degrees of deadrise - semi V Lowe-style
6. Year, make and model of motor - 2000, Mercury, ELTP
7. HP and gear ratio of motor - 40HP, 2:0
8. Manufacturer?s recommended WOT range - 5000 - 5500
9. Antiventilation Plate height above keel of boat if it is an outboard in inches - upper antiventilation is 4.5 inches above keel - lower antiventiliation is even with keel
10. Make, model, diameter, pitch and whether SS or aluminum prop - damaged prop was a mercury 10.88" dia. x 11" p.
11. WOT RPM and speed from each prop - ??? I don't understand this question. There is only one prop. Do you need the RPM for the rotation of the prop at WOT? Can I get this information from Mercury's website or iboats.com?

 

[junior1113]

Re: Advice on prop size for 40HP Mercury on 17HP Lowe Roughneck

yes rpm are important to know. how do you know if your within recomended range and geting max performance. id invest in a mini tach if no tach. hwsii should be able to give you a ballpark prop size with info you have.

 

[netsomnia]

Re: Advice on prop size for 40HP Mercury on 17HP Lowe Roughneck

Are you saying that the information that I gave you for question 8 was not sufficient? I have a tach on my boat and generally run my boat at 5000 - 5200 RPM. I could go higher to reach the maximum RPM rating, 5500, but I do not trust the accuracy of my tach. Please let me know if you need more information.

 

[hwsiii]

Re: Advice on prop size for 40HP Mercury on 17HP Lowe Roughneck

Netsomnia, let me congratualte you on your response, that was fantastic information on the first try, in fact all I needed. With the heavy power to weight ratio of 45 # I can see why you were running an 11" pitch prop. I doubt you have a tachometer because with just 1 person in the boat you should have been overreving the engine. My recommendation is to get a 12" pitch prop as you will be able to get a little extra speed but not quite as much hole shot and when you are running lightweight it won't tend to overrev as much. I would recommend buying a Tiny Tach as they are only about $ 40 and simple to install. These are my numbers.

Boat and Motor

Prop Picker

H

 

[netsomnia]

Re: Advice on prop size for 40HP Mercury on 17HP Lowe Roughneck

hwsiii:

Thank you for your quick responses. I have a tachometer but it never returns to the zero after the engine is shutoff - I don't know if there's a zero calibration control or not. I do like it to glance at and subtract 1500 to make up the difference in calibration.

 

[hwsiii]

Re: Advice on prop size for 40HP Mercury on 17HP Lowe Roughneck

You are very welcome, and I would appreciate it if you would come back and post your WOT RPM and speed for my database.

H