Inboard prop size
 

I have been doing a search on proper prop size for the 23' inboard and was wondering what prop Miles offshore ended up with or any other suggestions. Is the correct prop a 16 x 17 with a # 5 cup? I bought my boat with the 4 blade and it is a dog. 17 knots burning 12 gph. There is no cup but after reading the post, I guess I need to trash the 4 blade and get a 3 blade. I have an old 17 x 17 3 blade I have as a spare. Can I use the 17 x 17 with say a #3 cup to get the same results as the 16 x 17 # 5 cup? I AM SO CONFUSED!!! :D

Classic Trade

Re: Inboard prop size
 

I forgot to say that I have the 351 ford engine in the boat and I believe it is aroung 250 hp. Thanks for the help.

Classic Trade

Re: Inboard prop size
 

Hey Author???- I am now turning a 16/15 old ragged spare wheel- the 4 blade was a dog for sure and i would be happy to sell it to any interested party :D I am going to by a 16-17 soon and that is what i plan on running- no cup- your wheel sounds fine (the 3 blade) make sure your rpms max out in the 42-4800 range and you should be fine- With lite fuel and the 3 blade i am burning 9 gph and getting 20 to 23 knots depending on tide/fuel etc with 2 people. hope this helps-

Re: Inboard prop size
 

Thanks for the reply. I am planning on posting pictures of my 23 but I am so computer stupid, I am not quite sure how to do it. So I need no cup with the 17x17? I thought a cup was good for the seacraft inboard. I know it is needed in football. :) :)

Arthur

Re: Inboard prop size
 

Miles offshore,

I'm getting around the same speed numbers as you, but I'm burning just a touch more at 10-10.5 GPH. what RPM are you getting that cruise at. I'm at around 3400 and swinging a 15x17 prop. This is also with a new EFI 350 rated at 350hp. I was hoping for a better cruise with that power. Any suggestions?

Re: Inboard prop size
 

R/R- you should be doing a heck of a lot better than that I think- you have quite a bit more horses than i do- how many rpms is it turning wide open??? I think you might be under propped a little- i think all that extra hp acounts for the little bit extra fuel consumption (maybe) . I normally run between 3K and 3200.


hey Auther- been waiting a while to see pix of your ride!!!!

craig

Re: Inboard prop size
 

I changed out my prop over the weekend to the 17 x 17 3 blade and what a difference. I am now running at a solid 20 knots at 3000 rpms. I think I may need to drop to a 16 pitch because my top rpm on the motor I could achieve was only 3900. I also had a noise and vibration that I have found to be the cutlass bearing. This should be fixed this weekend and then I will see what my top end rpms are and decide about the prop pitch. Thanks a lot Craig for helping me through this.

Arthur

Re: Inboard prop size
 

I have a 350, 315 HP and have a 17 x 16 with a little cup and turn around 4600. At 3000 I'm running 23-24 and burning around 9.5-9.8 gal's per hour. At 3200 I'm running 26-27 and burn 10.5 gal per hour. You need to have it proped so you can turn 46-4800 rpm with a good load in it (full tanks-three people) or the engine is lugging which is not good for it.

Re: Inboard prop size
 

Knot Working, Those are great numbers and where I love for this boat to be. If you are turning those numbers at cruise, what type of top end are you getting? How much room in the tunnel do you have with that prop, I think you need a minumum of 2" to be safe?

I think I'm going to play with some props soon.

Re: Inboard prop size
 

I don't know the exact measurement, but there is plenty of room ( I will measure) at real low RPM 1500-1700 I have a little rumble from prop tuberlance, but it is only in a real small range, and I had a little when I had the 351, 233HP. I turn at 4600 RPM 37 MPH. With the 4-barrel wide open around 17 GPH.

Re: Inboard prop size
 

I will be testing out a new 16-15 with some cup on it this friday, I will let you guys know how it works!

Re: Inboard prop size
 

I tried MILES OFFSHORE (Craig's) prop when I first put my motor in and could only turn 4200 rpm and the four barrel did not open all the way, the 17 x 16 gave me the 4600 that I was doing. I had a new tach and Meercusier make a digital for aboy $75 that I have to compare RPM's which gives a accurate reading, it wraps around one spark plug wire and ground. I have had trouble in the past with a Tach reading the wrong RPM's.

Re: Inboard prop size
 

Just got a call from the mechanic and he is finished putting in the new cutlass bearing. I may have to dodge rain drops this weekend but I plan on seeing what the new cutlass bearing does before I mess with the prop. Normally this would not make a difference but the cutlass was in horrible shape. Vibrations were bad. Also, I am not 100 % sure the tach is all that great either. I still have lots to do, but I do love the boat. SEACRAFT FOREVER!!!!! :) :)

Arthur

Re: Inboard prop size
 

I have the plug in mercruiser fuel management system with all the goodies that go along with it, but I have never tested that tach against the regular RPM tach. I'll check it this weekend to see if there's a difference as well. I too am going to check wot RPM's. Thanks again for the help guys!

Re: Inboard prop size
 

It sounds like all you guys are cruising at more RPM's than me. I tend to cruise around 26-2800 RPM's. Current depending i make about 17-20 knots. I don't know exactly what size wheel i am spinning but i don't have any viberations. Does this sound like i am not running her at the best RPM range? I have a 1995 mercruiser inboard 260 hp, 350 small block chevy. Any thoughts??

Re: Inboard prop size
 

Chance 1234

I have that exact engine in my other boat and I find that the best cruise is 3150 rpms, just before the quadra jets kick in.

Arthur

Re: Inboard prop size
 

Well I found out that my Mercury computer does read about 2000 RPM's lower than the reqular tach. Unfortunatly while moving from one spot to another the ethenol issue I've been having all season finally got me. I got a tow back to the dock and it looks like the brand new tanks may have to be drained.