As a 16yo on the tinnie we used a shifter to slightly bend the trailing edge for cup. reduced cavitation and increased the speed. We then found cheap clever props and got to 70km/h in the tinnie. We had to stop because the tinnie became the welding shops dream customer...
Awesome video. Been looking for something like this for years. Been working on a mates 3.7m tinny with a 3 cyl 40hp yamaha. We've added a tunnel and raised the motor 150mm the prop shaft is level with the old bottom now. We're now playing with venting the tunnel at speed, but need more grip. I think this is where cupping will come in. Thanks for the info mate.
I’m glad I found this channel! It’s got some great content mate well done!I’ve found especially with rc boats The leading edge of the prop being larger like the original gives traction and the cleaver with the blade removed from the center point gives lift
@@25hpboatracerman yeah the rc stuff can be a ball! But that whole other life that I went a bit too far with! it’s funny just after writing that comment about the prop lift I saw a vid on tunnel hull props that contradicts what i said! although it’s with an altogether different design, a 4 blade razor type prop with the start of the leading edge protruding from the hub! And pointed tip for rougher water, I guess it’s got less to do with the initial interaction with the water at the blades than the projected angle of the water than I thought!
@@25hpboatracerman also I’ve been pondering the idea for a while to build a hybrid outboard motor, just by mounting a big fkn out runner onto the flywheel! It’s potentially a large alternator too! but suppose I took a 10-20hp bldc motor and mounted it onto my 1960s evinrude 9.8 how’s the gearbox going to like instant 25-30 hp and a big pitch prop?? lol! I’ve got a heap of other motors though too
Hi mate, Too easy, just take it easy with your mods, It’s better to do little changes at a time to see if they are helping or if you a losing speed or performance in some way. Cheers 🍻 Aussie Boat Guy 😎
Fantastic video!!! Great timing as I’m trying to add cup to my prop and I’ve been doing it wrong haha I now have a better idea of how to do it properly thank you!
Hi Champion, You are correct 👍 The only thing with what I was trying to achieve is 90% of the time lowering the motor looses speed so got around the issue with better prop design. Cheers 🍻 Aussie Boat Guy 😎
I've got a beater prop I'll be modifying this weekend just for fun. It started me thinking about props though. Why don't all props come cupped, what's the purpose of the big sweeping edges? Why aren't all props cupped? Is it all due to efficiency? Just surprised how hard it is to find a cupped race oriented prop for a small motor like my Johnson 25.
Hi Mate, Good questions 👍 Well most props come with no cupping or very small cupping as when a prop is fully submerged it is harder for it to aerate, same story with the sweeping blades. When you go to a racing propeller and start running some of the propeller blades out of the water (surface piercing props) then the design needs to change to include more bite and less chance of aeration. Also a racing style propeller run at full depth is not efficient and would slow the boat down a heap. Cheers 🍻 Aussie Boat Guy 😎
Thanks for this, have acouple older props...think Ill give it a try., never really knew where to start. The cupping part, think thats where Ill mess up...probably doesnt take much.
Hi mate, Yeah, cupping is important not to go too big. Remember you can always add more. A nice little tight cup mostly is all you need. Cheers 🍻 Aussie Boat Guy 😎
I have a mariner 5hp on a 8foot terjesen jolle and i have a topp speed that is 16mph - 30kmt. Is there someting i can do to the motor or prop to get more speed easy??
Hi Mate, The easiest thing will be propeller mods, removing as much weight as possible from your boat and raising the motor slightly, make sure it’s still picking up cooling water. Cheers 🍻 Aussie Boat Guy 😎
Looking at doing on old 6hp Johnson is there any way you can send over the template you used for your prop ? Maybe email or something like that ? Awesome videos by the keep the great work coming
Hi Mate, Really appreciate your comments 👍 Unfortunately the template will not suit your prop. I would start with thinning and a small cup and see how it runs. Also see if you can find an 8hp carburetor that suits your block. cheers 🍻 Aussie Boat Guy 😎
Hi Mate, It is definitely harder than an alloy but same method. I have used heat in the past too on stainless. You have to be careful as it is easy to wreck a stainless prop, you still want your cupping to be a small radius and not move out onto the blade too far (just on the tip) cheers 🍻 Aussie Bowt Guy 😎
Hey man love all your videos and all the information that you share I have a question that you may have the answer to with the mercury Tohatsu 4 and 5 hp‘s what is the difference between the 4 hp and the 5 hp Is it just the CDI
Hi 👋 If we are talking two strokes then - Yeah, believe it or not, I’m not really sure. I have had a 4hp as well (but not fully apart) and the carburetor was the same with the same throat size etc. It must be something internal like ports or reed stops not opening as far but I have not had a 4hp block apart. Can’t even remember how many 5hp I have done though, they are a lot more common. CD packs are the same from what I saw. Cheers Aussie Boat Guy 😎
I have a 15 pitch and 17 pitch propeller, but I figure what I need is a 16. Not widely available. Do you suggest I grid off the cup on the 17 pitch and cut the blades as per your video, or add cup to the 15 pitch?
You can try either. If your 17p is too much then removing some cupping is a good start but I would reduce the diameter a bit too which will bring revs back up, as per my video - if you remove just that leading edge of the blades you actually increase pitch. So with the 17p leave the leading edge of the blades, remove some cupping and some diameter, only a bit at a time and test it. With the 15, you could do exactly what I did in the video, my 9p ended up at just over 10p. You can always have your props re-pitched too which is actually big expensive and a good option too. What size motor? Cheers Aussie Boat Guy 😎
so i have a 9.9 mercury and and a rubberboat. how much difference would it make to modify my prop. and what prop pitch do you think is best for top speed. i reallt like your videos by the way
Cheers mate, Thanks for your encouragement. It really depends on how heavy your boat is and what rpm your getting with the prop your running now. If your motor is already reaching max rpm (around 5500) at full throttle then modifying the prop may slow you down as the motor will have trouble spinning it. If your motor is over revving then modding your prop is the go and you could get more top end speed. All the best, Aussie Boat Guy 😎
Hi Mate, You would only remove the flair if going full performance and you have a good rake on the blades with blade trailing edge cupping. That flair stops aeration and cavitation. Cheers 🍻 Aussie Boat Guy 😎
Hi mate. Cheers 🍻 Yep, done it to merc stainless props too. Just try and get the cupping small and tight up on the trailing edge. You can always add more if needed You don’t want a big radius cup. Thanks Aussie Boat Guy 😎
Great vid again mate, I have an old alloy Mercury Spitfire 4 blade prop as a spare for my 60hp 4stk running the command thrust gearing . I am running the same prop but in stainless at the moment same dia and pitch, 13.8 × 13p . They both max out at 5300 rpm but my motor is good for 6000 rpm, I was considering doing this to the old alloy prop to see if it will give me a better top end and ideally 5700 - 5800rpm would be ideal. Do you think this is something that is achievable ?
Hi mate, thanks 😊 I would be just removing some diameter then balancing, no more cup or your revs will drop even more. So I mean actually reducing the overall diameter- so say bring it down 1/2 an inch 1/4 off each blade, balance then try. You can do it in a few stages but reducing diameter will bring your revs up and possibly gain you some top end speed. Reduce the whole blade, not just the section I covered in the vid. Cheers 🍻 Aussie Boat Guy
Hi 👋 Absolutely mate. Sharpening the little 6hp propeller leading edge will help too (to sharpen only take material off the back of the blades) Keep the cupping very small as it increases pitch, I would try just sharpening first without changing blade shape or adding cupping as the old 6 Johnson doesn’t have a lot of torque. Cheers 🍻 Aussie Boat Guy 😎
Hi mate, Yep, sorry, it’s been on the back burner for ages. It’s still going to continue and is further along than last vids. I should do a vid to catch up 🤷♂️ The whole build stopped completely when I had some crappy medical issues that lasted a long time (pain is still an issue 🤦♂️🤦♂️) I am obviously getting way better as I’m tinkering with outboards, props and welded that tinny together. I am feeling like the wasp will kick off again in a few months. Cheers 🍻 Aussie Boat Guy 😎
@@25hpboatracerman a catch up vid would be great mate, looking forward to seeing the end result (pull ya finger out 🤣) I’m in the middle of a V17L rebuild, I know how much time it consumes. Cheers mate ✌🏽
Hi mate, You are correct, I should have the prop better supported a lot of the time while working on it. What do you mean unfamiliar with power tools? What power tools are you talking about? Are you trying to be rude? Or am I not understanding your comments? Cheers 🍻 Aussie Boat Guy 😎
good stuff mate. I'm running a stock prop on my 15hp tohatsu it goes real well. I might upgrade to a stainless prop soon to get a bit more out of her in a different pitch.
Hi Mate, cheers 🍻 yeah, love trying props, did the same recently with my 18hp and the stock alloy ended up being faster which surprised me, that’s a first for me, normally the stainless is the winner. all the best Aussie Boat Guy 😎
@@25hpboatracerman one question how do I go making my 15hp tohatsu in to a 18hp cant seem to find anyone around here to do it for me. I was thinking to try out a new prop to go a bit faster. But I will love it to be set at 18hp of Couse. 😀
@@bradleyfarquhar2023 Hi mate, Unfortunately the 15hp tohatsu along with the 9.9hp tohatsu are a smaller capacity block at 247cc and the 18hp is 294cc If it was a Mercury 15hp built by Tohatsu it would be the larger block as they restricted the 18hp and called it a 15hp. If you look on my channel, I put a video up comparing the 9.9hp and 15hp block to the 18hp block. Ps: the 15hp tohatsu still goes very well, not much in it really compared to the 18hp. The 18hp has a bigger carburetor too along with bigger ports etc. Cheers Aussie Boat Guy 😎
I got to ask, do you work in the propeller industry? , what your doing is some good industry reveals , thank you for showing what I'm not allowed to show
Hi Mate, Thanks 😊 Not in the industry but have been fully into this stuff for a long time, played with props, modified props, built props but not for clients, just for learning and for my boats over the years. cheers 🍻 Aussie Boat Guy 😎
