Newb here with a question on props

[ToneDef]

Sorry if this is in the wrong section. I am new to the forum and I am building a small hydroplane. Unfortunately the design is not class-legal per APBA's definitions, but I see it as a jumping off point for what could potentially be a fun future in boat racing. I've got a Nissan NS15B2 for power and I am looking for a prop and was told that for this sort of application, a cleaver style would be best and he told me to check out Ron Hill Marine! Then I found this site and that Mr. Hill is the man here. Anyway the engine has a 14 spline shaft, thru hub exhaust, and wants to run 4700 min. RPM and 5500 max. RPM @ WOT. Mr. Hill, do you build custom propellers to suit any application? Would I be best off waiting until I have run the boat a bit (she is about 1 month to completion) to see what I'm looking at for MPH and then talking prop?

[Ron Hill]

Got lots of props for you and others with 14 splines. But may need to see the prop first.

Call me Ron, unless you are my daughter-in-law (LOL) or one of my nold students....

[ToneDef]

Thanks Ron. Here are some pics of the prop. It's 9.2x8.5


http://img695.imageshack.us/img695/3261/0417001307.jpg


http://img340.imageshack.us/img340/5638/0417001307a.jpg


http://img695.imageshack.us/img695/2695/0417001308.jpg


http://img140.imageshack.us/img140/193/0417001308a.jpg

[ToneDef]

Ron what is the avg. cost for one of your props?

[ToneDef]

nobody?

[capnzee]

If nobody wants to step up here, I would suggest that a good stainless prop for your engine would come in at 200 to 350 bucks. (maybe less if the prop has been used.)This may be more than you want to spend on something that may add as little as 5 to 10 mph on your rig, depending upon what you have built. Before you can build the prop that you need, you will have to try what you already have (which isn't much), but it is a starting point. If your boat is in the building stages you may want to think about the transom height. With a planing type, low drag hull, you will get about 90 per cent of your total drag from the lower unit. The higher out of the water you can run your unit, the less drag you will encounter and the faster your boat will go--the problem here is two-fold. No.1, your engine is not built to run at a height that you would like it to--the water pick-up is simply too high and if you get the engine up where you like it, you most likely will not pump water and you will overheat. No.2, your present prop is not designed to run on the surface, or for that matter partially out of the water. Why don't you ask "Mr. Hill" if you can buy a stainless prop from him that is about the same diameter and maybe an inch or two more than your stock prop. I am sure that he will take the prop back in trade for another prop once you have tried it and have formed a basis for further testing. (this providing you have not dinged or screwed up the test prop.) Rod

[ToneDef]

If nobody wants to step up here, I would suggest that a good stainless prop for your engine would come in at 200 to 350 bucks. (maybe less if the prop has been used.)This may be more than you want to spend on something that may add as little as 5 to 10 mph on your rig, depending upon what you have built. Before you can build the prop that you need, you will have to try what you already have (which isn't much), but it is a starting point. If your boat is in the building stages you may want to think about the transom height. With a planing type, low drag hull, you will get about 90 per cent of your total drag from the lower unit. The higher out of the water you can run your unit, the less drag you will encounter and the faster your boat will go--the problem here is two-fold. No.1, your engine is not built to run at a height that you would like it to--the water pick-up is simply too high and if you get the engine up where you like it, you most likely will not pump water and you will overheat. No.2, your present prop is not designed to run on the surface, or for that matter partially out of the water. Why don't you ask "Mr. Hill" if you can buy a stainless prop from him that is about the same diameter and maybe an inch or two more than your stock prop. I am sure that he will take the prop back in trade for another prop once you have tried it and have formed a basis for further testing. (this providing you have not dinged or screwed up the test prop.) Rod

I've got a jack plate which allows me to raise the engine to the point where my prop shaft centerline is in plane with the bottom of the boat (if I wish to go that high) as well as adding 4" of setback to address the engine height, and I am waiting to hear back from Bob's Machine on a nose cone/low-water pickup to address the issue of drag and water.

I am actually relieved to hear that a good SS prop is in that range, I was worried I would be looking at $600+

As far as the (relatively) small MPH gains being worth it, to me they are. I came into this build with one goal in mind: 50 MPH. Will I make it to that? Probably not. But am I willing to do everything I can to get close? Hell yes. If that means dropping some coin on a good prop that's designed for this application rather than some stupid fishing prop, so be it. I suppose I probably am better off running what I've got first to establish some sort of a baseline.

Sorry if I came of as a bit of an *** before, that was certainly not my intention.

[capnzee]

It would be helpful if you would show us a picture or two of your project. Sounds like you are willing to put a few bucks in it--too bad you didn't take a look at APBA before you started building. Your aluminum prop is fairly easy to "work"--you may want to take a look at some of the stainless props used for racing and put a little "cup" along the trailing edge and just over the top of each of the blades. Don't get the cup too sharp or the aluminum will crack. Doesn't take much. Even though you don't have an APBA class to run in, Mr. Ron Hill is planning a "mini-enduro" scheduled for this fall, perhaps your boat will be ready and up to speed by then--I am sure that there is a class your rig will fall into! (that is if you have any racing in your blood-line--lots of guys simply like to ride around and think they are going fast--others like to prove it--which one are you?) Not trying to be a smart a**, just had my fill of "river racers" who like to talk big and sport a lot of t and a but are afraid to go chine to chine in a sanctioned race! R:)D

[ToneDef]

It would be helpful if you would show us a picture or two of your project. Sounds like you are willing to put a few bucks in it--too bad you didn't take a look at APBA before you started building. Your aluminum prop is fairly easy to "work"--you may want to take a look at some of the stainless props used for racing and put a little "cup" along the trailing edge and just over the top of each of the blades. Don't get the cup too sharp or the aluminum will crack. Doesn't take much. Even though you don't have an APBA class to run in, Mr. Ron Hill is planning a "mini-enduro" scheduled for this fall, perhaps your boat will be ready and up to speed by then--I am sure that there is a class your rig will fall into! (that is if you have any racing in your blood-line--lots of guys simply like to ride around and think they are going fast--others like to prove it--which one are you?) Not trying to be a smart a**, just had my fill of "river racers" who like to talk big and sport a lot of t and a but are afraid to go chine to chine in a sanctioned race! R:)D

Heh I hear you on the "all show no go" guys but I'm a racer through and through, from BMX as a kid to bangin' bars on the motocross track currently, I like to prove that I can hang and hopefully I'll get the chance to do that with this boat as well. If she ain't good to go by fall, something seriously ain't right! A mini enduro sounds like something I'd definitely be interested in partaking in.

Here are a few of the most recent pics. I've got the bottom and side planking on now.

http://sphotos.ak.fbcdn.net/hphotos-ak-snc3/hs281.snc3/27689_1253734223566_1235850002_552825_3131356_n.jp g

http://hphotos-snc3.fbcdn.net/hs281.snc3/27689_1253734343569_1235850002_552827_7956778_n.jp g

[capnzee]

It looks like you are doing a real nice job--got plans or are they in your head?
Looks like a shallow V up front to a flat bottom in the rear?? Be sure and get some good support on that transom--tie it in real good cause it is going to need a lot of strength to support that engine on a jack plate. Rod

[ToneDef]

Thanks, I'm building it from a set of Glen-L plans. It is a shallow vee up front and not-quite-flat in the rear; there is a very slight radius to it. They call it a monohydroplane.

[capnzee]

Glen L has been around for a good many years! Hope you are ready for the pounding you are going to take from that flat bottom. Are you planning on kneeling or sitting?
Now that you are familiar with this forum you may want to shift down to "SHOW US YOUR BOAT" and post on that thread.
Those Aussie guys have some great pictures and some great ideas for boats similar to the one you are building--check out the V-bottoms and how they ride--check out their props and what they have to say about them, you may want to make a few changes. As I said before, Glen L has been around for years and a lot has changed since he started publishing plans. :)Rod

[ToneDef]

LOL yes I hear the hulls can be pretty rough even on flat days. I'll be kneeling so hopefully I can use my legs to take some of the shock. I saw some of those mini V boats in the pictures section and all I could think was "where can I find plans for one??"

[Chairman]

LOL yes I hear the hulls can be pretty rough even on flat days. I'll be kneeling so hopefully I can use my legs to take some of the shock. I saw some of those mini V boats in the pictures section and all I could think was "where can I find plans for one??"

May I humbly suggest you take a look at my site? www.dillon-racing.com

[ToneDef]

Well I believe I have found my next build! It appears to be 1/2" marine ply?

[capnzee]

I know you are going to hate to hear this, but I believe you can "save" the boat you have started on. It would not take a lot of work to roll the work you have completed so you can work on the bottom, remove the stringers and build a Vee bottom in place of the flat bottom. I'll bet you could get one of the guys like "chairman" to assist you on this. A flat bottom may be a little faster, but in today's water it sure gets rough--adding a Vee to what you have would also make a little deeper boat and you could think about sitting instead of kneeling. Feel free to say "no thanks, I'd rather do it my way!" and I must say it looks like you are doing a great job of building. My dad and I built a boat similar to what you are building way back in the 50's (tells you how old I am). The first one was out of Popular Mechanics, it was called "SKEETER", then we built a second one with non-trip chines (much like the one you are building) What I am trying to say is what you are building is a very old design--I would bet the transom is designed for a 15" mid-section engine and yours is most likely 20 inches.

[ToneDef]

I know you are going to hate to hear this, but I believe you can "save" the boat you have started on. It would not take a lot of work to roll the work you have completed so you can work on the bottom, remove the stringers and build a Vee bottom in place of the flat bottom. I'll bet you could get one of the guys like "chairman" to assist you on this. A flat bottom may be a little faster, but in today's water it sure gets rough--adding a Vee to what you have would also make a little deeper boat and you could think about sitting instead of kneeling. Feel free to say "no thanks, I'd rather do it my way!" and I must say it looks like you are doing a great job of building. My dad and I built a boat similar to what you are building way back in the 50's (tells you how old I am). The first one was out of Popular Mechanics, it was called "SKEETER", then we built a second one with non-trip chines (much like the one you are building) What I am trying to say is what you are building is a very old design--I would bet the transom is designed for a 15" mid-section engine and yours is most likely 20 inches.

I hear where you're coming from, and I do understand that it is an outdated design, but it's just a jumping off point; something to get started in fast boats. It would be a great deal of work to convert it to a V bottom at this stage, those pics are a few weeks old and the bottom is now all planked, and I am willing to bet the wood will tear before the West System bond breaks if I try to remove that planking. I enjoy building boats almost as much as I enjoy using them, so all the better if I find another design that I like to build right?

Even still, I could take the current design I've got, (plans include for a 9'6" model as well as this 8'3") and build that, modifying the transom and frames for a V bottom. It would just pain me too much to rip off all that 1/4" okoume and cut into her!

[JohnsonM50]

Id agree there, tearing it up will be hard on the brain. Id say finish-er up & run. Do you have boat experience? The other race skills will no doubt be in your corner but with boats go fast tech is harder to come by. Keep in mind wheels coast, water wont allow for much & is far more resistant than air. That & your going without the 5 or 6 gears of a bike. Pretty much a gear ratio & a props pitch against the resistance. Simpler machinery = more complicated to make go. Best advise is run it with what you have. Over pitching the prop will kill performances get up & go. When you get real rpms & speed to make an educated guess with then invest in a prop. Ive gotten good props on ebay in the $100 range, even less [thanks Ron] At the point where you seriously work to speed it up youll need to do it methodically. Every prop will have a different sweet spot on height & or angle. Take notes & dont make too many changes at once, you want to know what works to apply to your next move.
I started into this with a build too & learned my way along, one thing for sure is things often seem like they should be what they arent. 50mph is a tall order.. but not a pipe dream. The stock motor/prop set deep enuff to work yet hi as can be will probably get ya to the mid+ 30s. Good Luck :cool:

[ToneDef]

Id agree there, tearing it up will be hard on the brain. Id say finish-er up & run. Do you have boat experience? The other race skills will no doubt be in your corner but with boats go fast tech is harder to come by. Keep in mind wheels coast, water wont allow for much & is far more resistant than air. That & your going without the 5 or 6 gears of a bike. Pretty much a gear ratio & a props pitch against the resistance. Simpler machinery = more complicated to make go. Best advise is run it with what you have. Over pitching the prop will kill performances get up & go. When you get real rpms & speed to make an educated guess with then invest in a prop. Ive gotten good props on ebay in the $100 range, even less [thanks Ron] At the point where you seriously work to speed it up youll need to do it methodically. Every prop will have a different sweet spot on height & or angle. Take notes & dont make too many changes at once, you want to know what works to apply to your next move.
I started into this with a build too & learned my way along, one thing for sure is things often seem like they should be what they arent. 50mph is a tall order.. but not a pipe dream. The stock motor/prop set deep enuff to work yet hi as can be will probably get ya to the mid+ 30s. Good Luck :cool:

Thanks JohnsonM50, I've got a 1957 Whirlwind 16' runabout with a Johnson 60 Sea Horse as well that's currently in the water, she runs 40-45 MPH, but we've got the engine de-tuned a bit for longevity reasons. Also I forgot to add the engine is a 18" leg, and I've got a jackplate with 6+" of adjustment

[Chairman]

Well I believe I have found my next build! It appears to be 1/2" marine ply?

Plywood thickness depends on the design. I've built tunnel boats with mostly 6mm (1/4") and a 3mm deck. My last tunnel had 3, 4, 5 and 6mm, trying to keep the weight to a minimum. My Mini Vee works just fine with all 5mm or 6mm. But my Pro Vee has a curvy bottom that is built up with two layers of 3mm.

The Mini Vee is really a fairly simple boat to build and a nice performer. Will go 40-42 with a 25hp OMC and aluminum prop (Mini GT class). Will go 46-47 with 35hp OMC (GT Pro class) and a Yamaha-style cleaver (courtesy of Ron).

I just bought a "real" cleaver from Ron, hope to be able to test that in a week or so. We're hoping to push GT Pro to 50 mph.

[JohnsonM50]

Thanks JohnsonM50, I've got a 1957 Whirlwind 16' runabout with a Johnson 60 Sea Horse as well that's currently in the water, she runs 40-45 MPH, but we've got the engine de-tuned a bit for longevity reasons. Also I forgot to add the engine is a 18" leg, and I've got a jackplate with 6+" of adjustment
The jackplate Im sure will be useful to determine best run height & the set back might be an advantage. One thing youll have to work out is the 'ride on the edge' but not porpoise [at speed] thing & I dont know what effect the plate will have on that. You would have to consider at some point beyond the height determination that to make the transome that height & eliminate the weight of the plate if its heavy. If it isnt heavy the setback will still effect weight distribution.. for better or not? What Id do is build the transome hi to begin with so when you get set up you have the option of direct mounting at a height close enuff to shim up to fine tune. In adjustments of the motor, the faster you go the more critical small increments will be. As far as racing "chine to chine" as Capnzee wrote theres several directions you can go, all of them cool stuff.

[ToneDef]

The jackplate Im sure will be useful to determine best run height & the set back might be an advantage. One thing youll have to work out is the 'ride on the edge' but not porpoise [at speed] thing & I dont know what effect the plate will have on that. You would have to consider at some point beyond the height determination that to make the transome that height & eliminate the weight of the plate if its heavy. If it isnt heavy the setback will still effect weight distribution.. for better or not? What Id do is build the transome hi to begin with so when you get set up you have the option of direct mounting at a height close enuff to shim up to fine tune. In adjustments of the motor, the faster you go the more critical small increments will be. As far as racing "chine to chine" as Capnzee wrote theres several directions you can go, all of them cool stuff.

The jack plate weighs under 10 lbs, so it isn't bad, But what you said makes sense, I will run with what I've got and make adjustments accordingly.

[JohnsonM50]

[QUOTE=ToneDef;90589]The jack plate weighs under 10 lbs, so it isn't bad, But what you said makes sense, I will run with what I've got and make adjustments accordingly.
QUOTE]Yeah 10s no great amount. The 'fishing' gear foot is designed to push a varied load at moderate speed so a light load will usually yield a only little more speed & alot more pickup. The motor will only spin so fast & the prop will never exceed its inches of pitch per R but always fall short. There being your biggest obstacle, the prop. Count on trying a few at least. One thing to know is to find a wrecked prop that fits & salvage the inner hub. This can sometimes be used to adapt a 'righty' speed prop. Ive seen it on another boat & did it on my pals hydro.. run a non thru hub prop. It -can- work with the thru hub, no guarantee on it tho. There's a couple formulas for whats happening with your prop concerning slip & drag.. What I do is take note of accurate speed. Multiply pitch by RPMs [= inches per minute] Divided by 12 [=feet per minute] Times 60 [=feet per hour] divided by 5280 [= mph*]
* then determine your gear ratio.. Example my OMCs turn 21 times at the motor per 12 at the prop so 12 divided by 21 = 0.571:1. Multiply 0.571 by [mph*] to get potential speed... The MPH you would go if there was no slip or drag 'perfect world'. Compare it to real speed noted before & see what % of efficiency your prop operates at. Ive got 2 cleavers that work at about 90% so Id call them a good style to try but not discount others. The gain you will get out of a little motor work will pale in comparison to a good prop set up optimally. To get 45mph out of a 30mph motor you would have to more than double your output at the trade off of the low end torque you need to get on plane & maintain speed while the water simulates going uphill in sand on motorcycle wheels. :eek: Mike

[ToneDef]

Well Bob's Machine was a no-go on the nose cone/low-water pickup. Apparantly the water cavity on the Nissan 15 is to small to drill and tap into. Anyone else make nose cone/lo h2o kits for small outboard?

[JohnsonM50]

Well Bob's Machine was a no-go on the nose cone/low-water pickup. Apparantly the water cavity on the Nissan 15 is to small to drill and tap into. Anyone else make nose cone/lo h2o kits for small outboard?

Ive dont that a different way but you still have to tap into the motor somewhere before the pump & probably close off most of the hi water pick up. Till you have a surface running prop you wont need this.
http://i35.photobucket.com/albums/d151/mes355/DSCN0369.jpg
http://i35.photobucket.com/albums/d151/mes355/026.jpg
http://i35.photobucket.com/albums/d151/mes355/019.jpg
race props also have height limits, at some point they will just cavitate & not grab. You will have to scream the motor for several seconds till it grabs anyway if your set up well enough to get the speed intended from a prop. Very ruff on the motor & important that it get enuff :cool::cool::cool:

[ToneDef]

Ive dont that a different way but you still have to tap into the motor somewhere before the pump & probably close off most of the hi water pick up. Till you have a surface running prop you wont need this.
http://i35.photobucket.com/albums/d151/mes355/DSCN0369.jpg
http://i35.photobucket.com/albums/d151/mes355/026.jpg
http://i35.photobucket.com/albums/d151/mes355/019.jpg
race props also have height limits, at some point they will just cavitate & not grab. You will have to scream the motor for several seconds till it grabs anyway if your set up well enough to get the speed intended from a prop. Very ruff on the motor & important that it get enuff :cool::cool::cool:

That looks like a setup I could try if I end up with a race prop. In the 3rd pic, it appears that there are some small holes drilled in the plate you have blocking off the hi water pickup? Is this so it is not 100% closed off?