yet one more guy that needs help with prop selection

[sprouticus]

ok...I have a 16 foot runabout with a 70 hp evinrude. I carry 2 batteries, up to 70 litres of fuel, and up to 850 lbs in passenger wieght. I have the boat for fishing, and tubing, (occasionally skiing), and of course cruising. My last prop only got me up to about 27 MPH. It was a little chewed up when I bought the boat, so I think I should be able to go faster with a new one. I am now forced to buy a new prop (underwater obstruction today) and was wondering what the experts would advise for me in regards to pitch. I plan on using the old prop as a spare as it still works, (although even slower) and this new (great deal) on a boat is eating up all my extra cash, and then some since I got it. Thankyou in advance for reading.

 

[b.gagnon]

Re: yet one more guy that needs help with prop selection

What RPM are you turning @wot????

 

[danie]

Re: yet one more guy that needs help with prop selection

What are the specs of the prop to be replaced.

 

[QC]

Re: yet one more guy that needs help with prop selection

Take a look at the WOT and prop selection threads in the Engine FAQ section. This will help you a lot.

 

[Mahoney]

Re: yet one more guy that needs help with prop selection

With that kind of load on a small 16 Ft boat, you should probably plan on having 2 props available for the kind of boating you are going to do for the day.<br /><br />Prop selection is a piece of cake if you know 3 facts. <br />1.What is your current WOT RPM with the prop you have on now?<br />2.What is the diameter/pitch of your current prop?<br />3.What is your engines WOT RPM Range?<br /><br />If answer to 1 is in the uper range to the answer of question 3, then you technically have the correct prop for the boat given the load you tested question 1 with.<br /><br />If your current WOT RPM's fall short of Engines recommended RPM, you should go down in pitch. Usually 1 inch decrease in pitch = ~200 rpm higher at WOT. Works the same the other direction.

 

[sprouticus]

Re: yet one more guy that needs help with prop selection

I do not know my RPM's as my boat does not have a tach. I plan on purchasing one, but it will have to wait a bit as I just got the boat and my budget is already strecthed pretty thin on it. My old prop was a 13 1/4" with a pitch of 17. It plained the boat, but with me and 3 buddies in the boat, we had to lean to the front to get the bow down. I adjusted the locking setting on my motor as my trim does not seem to be working anymore. Thankyou for trying to help me guys, I hope you can make sense of what I am saying because I do not know all the correct terms, etc. I have tried to research this for myself, but because I have no experience, or a tach, It is impossible for me to choose the right one with any certainty. I was hoping someone here might have a similar setup as me and could tell me what size prop worked for them. Thanx again for being patient.

 

[sprouticus]

Re: yet one more guy that needs help with prop selection

one more qucik question.............what should I expect to pay for a prop, and is it possible or even worth it to rebuild it???..I have been checking prices on the net,and they seem to be about $80-$100 american. Twice that or more for stainless steel. We have a guy in my town that rebuilds/sells them. I would rather buy locally of course, just don't want to get ripped off.

 

[QC]

Re: yet one more guy that needs help with prop selection

Rebuild is a good way to go. Most of us have had props rebuilt and some of us many times . . . I would recommend that you buy a new one and then have this one reworked as a decent spare once you can afford it. Pricing sounds right. You could also show the local guy your existing one and have him quote that. Better ask him when he'll be done too, he could be very busy this time of year.

 

[sprouticus]

Re: yet one more guy that needs help with prop selection

thankyou for your help.....I ended up buying two solas props, pitched were 17 and 15. My boat can plane much faster, but I still think I should be able to get a higher top speed. It's a learning process I guess.

 

[Mahoney]

Re: yet one more guy that needs help with prop selection

You may want to try smart tabs as well, you can run a higher pitched prop(as long as you are in the recommended WOT for your engine) and you will plane much faster, no more"everyone to the front of the boat!"

 

[sprouticus]

Re: yet one more guy that needs help with prop selection

no more"everyone to the front of the boat!"<br /><br /><br />LMAO..its like you were watching me out there. <br /><br />excuse my ignorance.but what are smart tabs???...<br /><br />and does anyone have a clue what the recomended RPMS are for a 70HP 1977 EVINRUDE at WOT???<br /><br />the 17 pitched prop now gets me to 28 MPH, but the revs seem low......it planes pretty quick though. the 15 pitch planes right away, but the top speed is only 25 MPH, and the engine sounds like it used to with my old prop at WOT. this was a test with just me and my friend and our dogs........about 450-500lbs total weight plus gear. Shouldn't I be able to go 30-35 MPH??? I took a 65HP out for a spin and it reached 31 MPH with 3 of us in it. thanx again everybody.

 

[Mahoney]

Re: yet one more guy that needs help with prop selection

Smart tabs are fantastic! They are relatively inexpensive, and dirt cheap considering the performance improvement on a boat. for your sized boat you can prolly pick up a set for ~100-150 USD. They are basically automatic adjusting trim tabs for your boat(those flashy little plates on the back of a lot of boats, except these dont adjust using a hydrolic system and switches on the dash, but automatically as your boat picks up speed and puts more pressure on the plates.<br /><br />If running bigger props, this has a dramatic effect on how fast you get on plane and cuts down dramatically on the bow rise. I installed them on my 19 ft cobalt, Heavy boat, and it was like I put another engine in it. You wont gain top end speed, but you will be on plane in a heartbeat.

 

[Jdeagro]

Re: yet one more guy that needs help with prop selection

mahoney;<br /><br />Thanks for the testimonial. I you have not picked up top speed, then the pressure should be reduced until you do. About 2 to 4 MPH.

 

[sprouticus]

Re: yet one more guy that needs help with prop selection

sounds cool...can I get them at my local marina???

 

[xecutech]

Re: yet one more guy that needs help with prop selection

How hard are they to install? The smart tabs??<br />I need them bad, I have a 20' cuddy, so all the weight is behind the driver.<br />We have to have everyone come to the front to plane. I thought my boat was a p.o.s, but feel better now knowing it's not just me!<br /><br />Also, my boat has had a tendacy to lean to the left or right from time to time, will smart tabs help this as well?

 

[sprouticus]

Re: yet one more guy that needs help with prop selection

i don't know about smart tabs.....but I put on a new prop, and now my boat planes really easy.<br /><br />How banged up is your prop, it seams that even a few small dings can make a difference.or at least it did with me.

 

[sprouticus]

Re: yet one more guy that needs help with prop selection

just thinking......I am very new to this...but is it possible that you have water in your boat?????.........

 

[stevens]

Re: yet one more guy that needs help with prop selection

Take it from a guy that has 10 thumbs, the Smart Tabs were a breeze to install! Just follow the (almost) fool-proof instructions to the letter. I was a bit hesitant to drill holes in the boat, but am glad I got over it. These tabs do exactly what was promised, on my 21' / 2650 lbs daycruiser; lower planing speed, much less bow rise, and a more stable ride at all speeds.

 

[Mahoney]

Re: yet one more guy that needs help with prop selection

Tabs are a piece of cake to install. Took less than an hour for both measuring and remeasuring and installing. Make sure you dry fit them first while on trailer with all straps attached, ladder down(if applicable) to make sure you don't have an issue with placement after you are all done drilling holes.<br /><br />Nautijon, I did reduce the pressure on the plates and I think it helped, although I also replaced a bad plug prior to checking this, and increased my horses by about 15%, so it was definitely faster!<br /><br />I am going to keep tweaking, just because I like to.