PROPS - THE SIMPLE TRUTH ABOUT PROPS
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- Опубліковано 18 жов 2024
- Props - The simple truth about props is all you need to know to make the right decision on whether you have the right prop on your boat. The small boat captain makes prop selection simple.
Thank you very good advice it took me four props to find the right one for my 2019mercury 60h.p. bigfoot its 13.78x11 spitfire 4blade rev range is spot on and holds wellat sea regards and make some more videos 😊😊😊
Thanks mate. I'll get back into making more videos. I have just been away for work.
The big foot is a tricky motor to prop. Bigger gearbox means to can spin a bigger, heavier prop if needed. What sort of boat is it and is it very heavy for its size?
Thanks for the link to the prop-slip calculator...My Bayliner with 3.0 Mercruiser and 21p 2:1 ratio, 4600 RPM and 46 MPH off GPS gave me a -1% slip....which is AWESOME !
Maybe my Tach is OFF ...
Wow. Can't beat that Peter. My Brother used to have a Bayliner with a Mercruiser and Brovo sterndrive leg. Great boat. We used it to tow the kids on tubes when they were little. Loved it.
Undiluted information. Great video.
Thanks mate. Glad you got something out if it. Cheers.
Thank you so much for being clear and concise.
Glad it helped mate.
SBC
Excellent video, glad I found this channel 👍
Thanks so much for the compliment. I enjoy making the content so glad you are getting something out of it.
SBC
Great video ! Easy and simple 👍
Thanks mate. SBC
Awesome video thanks so much mate.
Thanks for the feedback.
@@smallboatcaptain1968 I have just upgraded my boat and have that same engine. I was so confused about props because there is some much info on what you need etc etc. Awesome video mate because I now understand what I need to do. My boat revs are low and I need to change that pitch. Keep them coming. I also shared your link into a few Facebook groups I am in because this is a common thread.
@@vman4220 Thanks so much mate. I agree. It is very confusing but facts are, there would be two or three props for 99% of all boats that would suit and picking the right one is all about getting that max rev range right.
Thanks so much for sharing it.
SBC.
@@smallboatcaptain1968 I have that same prop as you the 13-5/8x 14 so when you say down a pitch for lower revs I need the 15 to bring those revs up??
@@vman4220 A greater pitch will actually put more load on the engine and therefore lower the revs. So if your boat is over-reving slightly, the 13.5 x 15 is the go.
Great info mate
Thanks so much. Glad it all made sense.
Gday mate just wondering about 4 bladed props they make them for smaller and larger outboards saw them on the oz props sight when looking at hydrofoils any thoughts good bad ?
G'day mate. The idea behind a four blade prop is creating more torque. As you can imagine, a four blade grabs more of the water and therefore, makes the prop more effective at pushing a vessel at lower revolutions, particularly for heavy vessels. This is why many bulk carriers have a five or six blade props. But on a boat that doesn't need that extra torque, it slows it down due to the extra drag created by that extra blade. It may also mean that the engine will be under too much load so can damage the engine. So four blade props slow most boats down considerably.
So unless you have a pontoon boat or another vessel that is very heavy, I would avoid a four blade prop. However, if you need the low speed or low rev power than a four blade is ideal.
I used to work for a resort that had a number of vessels that I was in charge of and I put a four blade prop on a 90hp Merc Big Foot engine. This is a 90hp engine with a 115-140hp gear box and leg. The reason for the big foot engine and four blade prop was because it was on a floating concrete pontoon that we used to drive out into the water and use as a base for watersports. You'd never get this pontoon to plane so I used to drive it out at about 3800revs, anchor it up and run it back into the marina in the afternoons. The four blade prop on that was a cracker.
So there is a good reason why 99% of small boats have a three blade prop.
Hope that helps.
@@smallboatcaptain1968 thanks for the reply mate thought that i would ask and il stick with the three blade deposit on the new engine today .
@@crispernator Good call mate.
Talk to steve or yan at oz props they helped me and it worked ane didnt cost the earth regards 😊😊😊
Great video. I'm in the process of figuring out overheating alarms at WOL on a Yamaha 50 two stroke 1999 (Long reach).... Do you think the size of he prop is contributing to the problem? Its a 11.6 x 12 prop on a 4.55 m aluminium runabout. RPM is a long way off ideal range, getting to only 3500-4000 before it gets too hot (ideal RPM range is 4500-5500). I think its a heavy boat for the motor size (~350kg conventional monohull) and I think a bit more RPM would benefit the life of the engine... I was thinking about trying reducing the pitch of the prop, like a Yamaha G series 11 3/4 x 10 . Boat is regularly serviced, new impeller etc....Any advice appreciated.
Haha The Park Bad Boy. What a UA-cam Name. Always happy to help mate. Thats what this channel is all about. I just went online to see what props are available and you've done your homework. With such a massive rev problem, I would be trying to prop the pitch to around 10.5 but seems that you can't. So that prop is about all that you can try. I don't think it will get it in that sweet spot but it will help. I tried finding a 10.5 x10 for a 50 Yammy but they don't seem to make them.
Sorry I can't be more help Park Bad Boy. SBC.
@@smallboatcaptain1968thanks mate good advice. I'm going to take it out on a calm day and do some tests and workout if I go down to one or two pitches, either the G series 11 5/8 x 11 or even lower at 11 3/4 x 10....I'll keep an eye out for an after market 10.5 x10.
@@TheParkBadBoy Let me know how it goes mate. Its a tricky one.
Whoch one u would recomend me gor 8 hp 7.5 or 8.5with 7.5 its goingaround 27 Kmhi wonder would 8.5 make any diffirence at top speed
G'day mate. It depends on the boat. The 8.5 would work better if the boat is very light but if it has some gear in it and runs loaded up, the 8.5 would put too much stress on the engine. This will reduce the revs and slow you down.
Think of boats like manual cars that are stuck in one gear. IF you were stuck in top gear, you would never get on the plane because the engine is under too much load. Low gear would get you going but you would over rev and blow the engine. You have to find that sweet spot.
One way to find out is to try it. If it doesn't make you go faster or is too slow to get you on the plane, just use it as a spare prop and stick with the 7.5.
Hope that helps. Sorry I can't give you a definite answer.
@@smallboatcaptain1968 the boat weights like 150 to 200 kg. but i still think i will keep 7.5 since i got 30 kmh with it, think its good speed for outboard engine which is only 8 hp. thanks for answer. appericiate
Yeah good call. Seems like the best prop for the engine.
😂 if you can only find 2 or 3 options you're looking in the wrong spot mate
You must be a race/speed boat fanatic AJM. This channel is all about small boats and the basics. Off course you can get customised props and every reply you give is correct. You obviously know what you're talking about. But you must agree that to get an engine into the right rev-range on a small weekend boat setup, two or three choices will be all that is required unless that boat is way under or overpowered.
SBC
@@smallboatcaptain1968 I am indeed but that has nothing to do with the basics. You don't need a custom or race prop to get the right weekender setup. Power tech propellers sold by Aussie companies have plenty of stainless options. A stainless prop with cupping is going to grab the water better, allowing you to lift the motor and change the whole characteristics of any boat. All people need is the right information instead of being told there are not many options 👌🤙👍
@@AJM-0205 I totally see your point mate but I disagree. Custom stainless props on small weekend runabouts don't make enough difference to justify the cost and protentional damage to your engine. Not to mention to extra weight spinning on the end of the shaft. Get the rev range correct with the right standard pitch and diameter and you will be 90% sorted. I could make a video about the other 10% but for the average beginner boatie that watches this channel, it's not needed. That's my opinion and I understand you don't agree, and that's OK.
I used to run a watersports dept for a big resort in Queensland. We had a couple of ski-boats and our mechanic insisted we had shit props. They were stainless off course but just your standard Solas. We changed to custom props and it made no difference at all. We then changed to another custom prop and lost our high-end rev range unloaded. finally found a cup in a smaller diameter that gave up our revs back and it was better out of the hole but at the end of the day, I couldn't justify the expense so just stuck with Solas. We spent a lot of money to make a small difference.
I agree with what you are saying, the right custom prop makes a difference. Just not enough for a bloke like me to go changing from a $150 aluminium off the shelf job.
Oh sorry its a mercury prop and its alloy 😊😊