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Thread: F-100 prop selection

  1. #1

    Default F-100 prop selection

    So I have a 24' Hewes with twin f-100's. the boat currently has Solas 13-1/4 x 19 stainless 3 blade props on it. Not quite getting max rpm's out of motors, about 5200-5400 with full fuel and light load (although this early Hewes carries 160 gals).
    boat has sit for 2 years so it does have old gas in it, I dumped a bunch of sea foam in it and replaced timing belts (1300 hrs on motors).
    I'm going to "shock" treat the motors with an additive that yamaha sells to remove built up carbon & stuff, then change oil, plugs, filters. All that might improve performance but since I'm going to run the boat as a water taxi, I need to be hauling 7 people & gear.

    also will need to run alum props; I have a set of 3 blade alum 12-5/8 x 21 but won't that pitch decrease hole shot? Also have one 13 x 19 alum prop and one 13-5/8 x 13 prop, not sure how the previous owner ended up with un-matched sets.

    what do you guys think would be a better match for what I need to do? Max top end is not too important but since I'm not dealing with gobs of torque with the 100's, trying to keep the power band optimal.

    Thanks-JimJim

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    Put the 12-5/8x21's on and run it and see. With the bigger blades on the 21's not sure if you are going to pick up any RPM, because you are taking a bigger slice of pie.

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    Well, I know a little bit about this boat. I was the original owner. I was able to get 5400 with those solas props with full fuel and my gear. I was burning a measly 8 gph at a 26-28mph cruise. Dang I miss that!! I would love to have seen 5800, but i loved the efficiency. Ideally you want to be between 5500-6000. The 13x19P aluminum props (not sure where the other one went) would hit 6000 and would launch the boat out of the water. I suspect that they would be ideal for your application. The 12 5/8 x 21P were smaller diameter, but would take a "bigger slice" due to the increased pitch. I would hit about 5800 with those props with fuel fuel and gear. The 13-5/8 x 13P was my limp home prop. I could almost get on step when light with that prop. The stainless props gave the best economy, by far, but I can understand why you want to go with aluminum doing what you plan on doing. Those F100s are bomber motors!

    Off to go burn 23 gph out on the Sound!
    Spending my kids' inheritance with them, one adventure at a time.

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    If you are turning 52-5400 with 19's you are only going backwards with the 21's, max RPM will most likely be 48-5000 with those. At a minimum you should be trying 17's but you need to pick up 600 RPM and plan for a heavier load. If I had to put my money somewhere it would be 15 pitch props.
    Casey
    Yamaha Dealer
    Petersburg, AK

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    Default 17 pitch 4 blade

    I'd go with the 17p 4 blade props, stainless of course with the load you are planning on running... 21p decrease rpms.
    The emphasis is on accuracy, not power!

  6. #6

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    Will try the alum 21's tomorrow to see what differene plus or minus they make, and that's the only other complete set I've got currently.
    So no one has mentioned the effect that prop diameter has; is that not much of a factor in the equation?
    Will report back! Thanks guys!

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    Jim, While my boat is a little heavier and my motors are 115's, the prop selection should be similar. I top out at about 36 mph at 5800 rpm on flat water with 3-4 guys and full fuel and stuff for a day trip fishing.

    I just checked my 115's and I'm running 13.5 x 17 stainless on a 26' Alaskan. A little research online showed this is the same recommendation if I went with aluminum. I do know with 19's (and more so with the 21's) you are "overwheeled", meaning you're making your engine work too hard - hence not being able to get the rpm's up where they should be. The Yammies are phenomenal engines, but the motors will not reach their intended life lugging them like that.

    I seem to recall the aluminum props "flex" when stressed for a hole shot, but should perform the same at cruise. Remember diameter is the first number on the prop - YMMV, but I wouldn't increase the diameter of the props if you're not getting Rpm's up near the recommended rates, which I believe is 6,000.

    On edit: found the site I referenced for a description of pitch and diameter http://www.boatingmag.com/maintenanc...ropeller-pitch

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    Quote Originally Posted by Akfish1 View Post
    If you are turning 52-5400 with 19's you are only going backwards with the 21's, max RPM will most likely be 48-5000 with those. At a minimum you should be trying 17's but you need to pick up 600 RPM and plan for a heavier load. If I had to put my money somewhere it would be 15 pitch props.
    Well, that was just my experience with them. The 19s are stainless and a much larger diameter. The 21s are aluminum and a much smaller diameter. Rule of thumb is drop down 2" of pitch when swapping out aluminum with stainless of the same diameter. I am not a professional prop tester nor do I play one on TV. Just my experience with that exact boat while I put 1000 hours on those twins. What do I know, though
    Spending my kids' inheritance with them, one adventure at a time.

  9. #9

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    Well, never did get the boat in the water today. Weather turned windy this afternoon so spent the day doing other fix-its. Replaced rusty racer setup, installed new inspection plates, weatherstripped & new screws on some rattling diamond plate panels, replaced motor zincs, attempted to remove corroded-in-place brass threaded drab plug in the transom extension. Struggled with that one for quite some time; heated it up, the head was already rounded off, couldn't get a good grip on it with anything, even a pipe wrench, so drilled and tapped it for a temporary 1/4-20 for a drain plug. Wanted something bigger but couldn't get a decent sized drill bit & right angle drill to fit.
    also found that I didn't have the prop washers for the alum props, need those to take up space on the shaft.
    All in all a good day tinkering!

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    Quote Originally Posted by Big Jim House View Post
    also found that I didn't have the prop washers for the alum props, need those to take up space on the shaft.
    All in all a good day tinkering!
    I still have a set of those I believe. I think they are in the new boat. I will check this weekend if you would like.
    Spending my kids' inheritance with them, one adventure at a time.

  11. #11

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    No problem Pete, got some more today, thanks though and if they're extras, be glad to take em!

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    Quote Originally Posted by Big Jim House View Post
    No problem Pete, got some more today, thanks though and if they're extras, be glad to take em!
    I will bring them home.
    Spending my kids' inheritance with them, one adventure at a time.

  13. #13

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    also found that I didn't have the prop washers for the alum props, need those to take up space on the shaft
    Big Jim House or Pete,

    I have the same motors on our boat and I am running the Yamaha steel props. I do carry an aluminum prop as a spare and a couple of prop nut kits. The aluminum props require additional washers? I was not aware there would be a difference in parts when changing out steel props for aluminum. Please educate me.

    Thanks,

    Doug

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    Doug, I believe the solas props that are on the boat were actually set up for Mercs, but were also compatible with the Yamahas. The yamaha props required the "spacers" while the merc ones did not. I could be way off here, but I believe that is how it was. I also tried the black stainless yamaha props, but the solas that he has on there just gave the best all around performance. I recall turning a few more RPMs, though. I suspect the numbers go up once the older gas burns off.
    Spending my kids' inheritance with them, one adventure at a time.

  15. #15

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    Pete,

    I am surprised that the hubs are different between the Yamaha black stainless steel and Yamaha aluminum props. I never knew there was a difference.

    I would be in for a rude awakening if I needed to put the spare aluminum prop on miles from home and found this out at that point in time.

    Thanks,

    Doug

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    I guess I was a bit foggy with my explanation. The solas props don't need the spacers while the yamaha, both stainless and aluminum ones, required the spacers. This is just my recollection. I sold the boat that Jim now owns back in the spring of 2006.
    Spending my kids' inheritance with them, one adventure at a time.

  17. #17

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    Pete,

    Ok. Now I understand the difference you are referring to. Thanks for the clarification.


    Doug

  18. #18

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    Well hopefully tomorrow it will be all clear as mud will attempt a cruise after work, ended up working late and blah blah blah!

    Ak, would ya mind sharing any fuel #'s ? Also how many hours on your motors and how you like them! Thanks

  19. #19

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    Ak, would ya mind sharing any fuel #'s ? Also how many hours on your motors and how you like them! Thanks
    Big Jim House,

    I am not sure the numbers will be meanigful to your situation as we are running the motors on different boats, but here you go.

    Boat specs:
    Bay Weld 25' with walk-around pilot house, 18 degree deadrise, 60 gallon fuel tank, twin Yamaha F100 motors
    Rigged Boat, Fuel weight, no gear - 4500 lbs
    Props - Yamaha 13 x 19 Black SS

    On our trips, multi-day out of a base camp, with daily runs, I plan for mileage run. So my tracking numbers are in MPG. Optimal fuel burn for me is at 4200 - 4400 RPM's at 23-26 MPH with MPG ranging from 2.3 - 3.1. The MPG varies due to gear and people on board and the 18 degree dead rise hull. The 2.3 MPG would be 4 adults, 2 dogs, camping gear, food, water, extra gas, and fishing gear for a week. The 3.1 MPG is two people and no gear.

    Doug

  20. #20

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    Took her out last night after work, ran the 21 pitch alum props and ended up with 33 knots @ 5700-5800 rpm's. was planning on running to seldovia but too lively so poked around gull, Sadie, Peterson.
    i will say that the stainless props kinda spoil a guy, smooth. Was getting a vibration at diff rpm's but props are old and not pristine.
    thanks for your fuel #'s Doug. Different boats to be sure but helpful anyway.

    Seems the port motor idles too high, 1200 rpm's, didn't do it before the trip to the yamaha dealer and new timing belts. I did have a difference in wide open rpm's between both motors and mentioned it to the mechanic, said they would check the throttle cables, hmmmmm.

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