Casper's VW powered boat

[casper22977]

Hey eveyrone

I am new here and have a lot of questions,
Let me start with that this thread caught my eye because I just got my first mini this past weekend and it has an
1800cc vw motor, it is a DD with a 50in Ivoprop. but I am not sure how to tell what pitch it is. the hall is 10x6 and resembles that of the older style river master. it needs a little work on the motor so I cant put it in the water but it seams to be quite light so I'm hoping it will perform well. from what I have been told it should be around 75 to 80hp the way it is set up. If anyone can help with how to tell the pitch it would be a great help.

here are a few pics, this is how it was delivered.

[buster]

casper22977,

Welcome to the mini forum

I think you may have more engine than your 50 inch prop can handle. I think it may be a good idea to call Ivoprop (562) 602-1451, and ask them about pitch, and any other questions you can think of. I know it is not good to spin a prop much faster than 3000 rpm, and I think that engine could do that easily.

You are about right about that 75 or 80 hp VW engine, especially if yours has dual carbs. I am building a Tomcat and am using an 1835 cc VW microbus engine, and I was told about those same hp figures.

BTW, putting a VW engine on an airboat kinda disqualifies it from the "MINI" class since it is a CAR engine, (but nobody really cares) just go have fun with it.

Dave

[Papee]

Hello Casper and welcome to the site. Buster has a point, that prop sounds a little small. I wouldn't do anything though until you get it on the water and run it as is. The shorter prop may work for you fine but you will be turning it faster at 50" than a longer one. A longer prop running a lower rpm would not be as loud. On a side note, if you decide to go with another prop I know someone that would be interested in your 50".

I'm going to move this to it's own thread so it gets more attention.

EDIT: posts moved.

[casper22977]

Papee thanks for moving the post I was not sure how to start e new one yet.
My real consern so far is the prop but the motor did not run right it had a bad seal at the head causing a dead cyl. so I disasembled it to rebuild and freshen it up. it also had a bent spot on the motor stand so I am going to fix that while I have the motor off. when I get that done I will get it on the water and will know more then. The other owner did not have a tack on it so I donot know if they even gave any thought to how hard they turned the prop. I did mesure the cage and I could go to about a 56in prop with out cutting out the cage and replacing.

Dave,
I did call and they could not help much being that there is no part number. all I know tyhat it is the ultra light series prop, they are ajustable but they come in two pitch ranges.
and that is what I would like to find out, that way if it is not what I need I will have a beter idea what to replace it with, but with out knowing the pitch I have on bench mark to start with.


MIKE

[Duane Scarborough]

Casper,

Welcome to the forum.

Papee and Buster have already given you better advice than I could, so I don't have much to add.

What I have to say is not contradicting their advice, just giving you something else to consider.

Remember that "about" 3,000 RPM is going to be as fast as you'll want to spin almost any prop, and that you're "not" going to get 75-80 HP from that VW engine at 3,000 RPM.

You'll need a reduction drive, if you want to get all that you can out of it.

In an ideal world, you'd pick a prop, and engine. Then you'd find out what the prop's optimum RPM is. Then you'd find out what the optimum RPM is for the engine. With those numbers, you can decide on the best reduction ratio.

I'm not saying that you can't get decent performance with that engine in a direct drive application. I'm just saying that you can get much more with a reduction drive.

Duane

[buster]

Duane,

One question comes to mind, If your engine can spin a prop 3000 rpm with direct drive, what more could you expect from that engine/prop combo if you added a reduction? It seems to me you would need to change props also to gain any performance.

Dave

[Duane Scarborough]

Buster,

C'mon. You ain't as dumb as I look. Think about it.

Consider a "typical" engine, that's rated let's say, 80 HP at 5,400 RPM. You don't really think it'll produce 80 HP at 3,000 RPM, do 'ya? It might produce "about" 40 HP at 3,000 RPM. You'd have to see the numbers for that particular engine, but that's a good guess.

Now, if you let that engine reach it's 5,400 RPM potential, it CAN produce it's rated 80 HP.

Using a reduction drive, you can run the engine at it's rated HP RPM, while keeping the propeller at IT'S rated speed.

Example 1: An engine rated 80 HP at 5,400 RPM, coupled to an adjustable pitch prop rated at 2,700 RPM with a 2:1 reduction, could produce a lot of thrust, when you adjust the pitch to match.

Example 2: Now, couple that same engine directly to the same prop, but still limit the RPM to 2,700 RPM to limit prop speed. The engine would be running at half of it's rated RPM, and you'd have to reduce the pitch of the prop significantly to get there.

The end result would be that example 1 could produce "about" 3 - 4 times the thrust as example 2.

Compare it to a car's transmission. You're kinda' got it in high gear all of the time. I've got it in 2nd gear.

Duane

[buster]

Duane,

OK, OK, my mistake, I was just assuming it was a fixed pitch prop, or that it was set at max pitch. If the pitch is reduced then it will do 3000 with a lot less hp, I do know that much.

Dave

[Papee]

Let's get him Buster. For a minute let's use the 084s for comparison. I run mine using direct drive at 3200 rpm and everyone else runs a bigger prop and reduction drive. I have yet to see anyone with GPS proof, show me $1200+ difference in performance, the difference in $$$ it costs to go with a redrive.

In your example I see you using a redrive to get a motor at it's sweet spot, 5400 rpm. in this case IMHO it is good to use a redrive to get the prop turning at the right rpm. Now, if a motors sweet spot is already at + or - 3200 rpm what are you really gaining by adding a redrive? You will run the engine harder and will be less reliable again IMHO. You know I march to a different beat. In some cases I just don't think the benefits outweigh the price difference. Would adding a redrive to gain 400 rpm at the motor be that beneficial? Some engines need a redrive IE a 2 cycle to get the rpms of the motor to match the prop speed.

Again here we go with my opinion. I believe it is better to build a boat around an engine choice than building an engine to a boat. This is in reference to a mini of course, anyone can build a boat then throw a bunch of HP at it to get it going. I have spent a lot of time on my boat getting the engine tilt right as well as getting the weight distribution correct.

On another note, pertaining to the VW engines, I ran one back in the 80's and had trouble with the seals leaking because of the front to back thrust on the crank. Would I put a redrive on a VW? Yes, but not becasue of the prop matching but because of the bearings. A redrive would take the sideways pressure off the bearing making a VW setup more reliable.

[buster]

Papee,

I agree about the redrive on the 084. I ran my engine around 3400-3600 with the redrive, and I think it would spin that prop almost that speed without the redrive. I wouldn't want to turn that engine any faster anyway, so what's the point?

Also a question about the VW since I am now involved with one that I intend to run DD, off the pulley end. (There is an extra main bearing near that end). Do you really think a reduction would eliminate sideways pressure? It seems to me a redrive belt when adjusted properly, puts a great amount of side pressure on the end main bearing?

Also, the front to back thrust (end-shake we called it), If I recall was fairly easy to adjust with shim washers on the VW crank. Was It still a problem, when adjusted to specs, with the seals leaking? I'm working with stuff I remember from about 45 years ago, so I will use the CRS card if I am wrong here!

Thanks. Dave

[buster]

casper 2977,

I just happened to remember that I bought a digital level from Sears Roebuck for about $35.00, and It is what most airboaters use to adjust prop pitch. you should be able to read prop pitch down to a gnats whisker. It works good for that, and it will be a welcome addition to your toolbox if you do many "Honey-Do" projects around the house. It is very accurate, and also a neat gadget to have.

Dave

[Duane Scarborough]

Papee,

I agree that using a redrive on a 4A084 is subject to argument. It was designed to run at 3600 RPM 24/7/365. It's sweet spot really is probably somewhere around 3200 RPM. I don't know that, but will concede to the idea.

That is not the case with a 75-80 HP VW engine. It's sweet spot is going to be somewhere close to the 5400 RPM range. That's what I think anyway.

There's been many direct drive VW powered airboats built. Some of them perform decently. But I'd bet that no one can build a VW engine that can produce 75-80 HP at 3200 RPM.

All I was trying to say was that you can't get that level of performance with a VW without a redrive. Does anyone really need 75-80 HP on a mini? Probably not.

Duane

[Papee]

I don't remember them running that high rpm. I had a few, two early buses and a 63 bug. The bug didn't run and I had the dual port rebuilt. I ended up making it into a baja bug. The sweet spot on my Tracker is about 4500 but I'm not sure I'd want to run it that hard or how long it would last at that rpm. I guess our Buster would be the expert on that. Maybe I'm thinking wrong again, IIRC he dabbled with them?

As you can tell, I'm a simple guy, I try to get what I can out of a motor the cheapest way I can.

[buster]

I think Duane said it best with "does anyone need 75 or 80 hp on a mini, probably not".

I think a lot of airboats with reductions will get the most hp and thrust at 5000 plus rpm, but in the cars those engines came with, only run 2000 to 2800 rpm normally, but they do it for many trouble free years.

Papee, I don't claim to be an expert on the VW engine, I just used to build VW based Dune Buggys. I just put them together and stick an engine on the back, and very little else if I could help it. Any engine work I did was purely maintenence, and to get it to go.

[Papee]

That's pretty much as far as my knowledge of them is. When I was young, I would go down to our local garage and work for free(15-16 yrs old) The old man taught me a lot, he was a big VW mech but I don't remember much other than how easy it was to get an engine out. Haven't thought about that in a while, wonder how many kids would work for free now days.

[casper22977]

hay everyone,

love the debate on vw's I agree with Duane that I see no reason to have 75 to 80hp on a 10ft boat but think of it this way the vw's were geared to run about 2900 to 3200 rpm at crusing speed, and were made to do so with a good bit of reliability for many years, heck we still see them all over to day. I personaly dont think i would want to twist one any harder than that for very long, atleast not with out puting mager money in very goog crank, rods, and pistons a car motor is not desined to be twisted that hard for long periods of time anyway. That being said if the vw motor runs 35 to 40hp at 3000 rpm, than I should be able to get about the same performance as a 40hp with a redrive, in theory? After all 40hp is 40hp no matter how you get it right? The only question is what kind of tork will I get? Either way if I can get it all figered out I should be able to get the performance I am looking for. after all I am not trying to create a rocket ship, just a boat that will get me, one other person, some camping and fishing gear to a good spot to fish.(and back to the dock)



buster,
looks like we are going to have some trial and i am sure some error in are near future. thanks for the tip on the level i am going to look in to that. I am not sure what to say about runing the prop off the pully end, but kick this around you said you are going to run it dd, the crank on that end of the motor is apx. 1.5 in diameter do you think it will hold up to the abuse of the prop? the flywheel end is almost 3" in diameter and very short.

boat porgress,

I got the motor tore down and it all looked good but the head seal, so that is good news now I am just waiting on the rebuild kit to get here so I can put it back together. I also got the motor stand rebuilt and levaled the motor boy was it out of wack I really have no Idea how they ever controled this boat befor. this week end I hope to finish up the welding on the riging, light mounts,and new stearing, get it panted and ready to put in the fresh motor. boy I cant wait.

MIKE

[buster]

Casper,

I know the crank is narrower on the pulley end, but it does have a second main bearing very close to the end bearing. Also, the heavy flywheel is on the opposite end. My reasoning for using the pulley end is that a lot of experimental aircraft are doing it that way and getting by ok. My boat will probably never get that far above the ground, so I feel quite safe Also since I just passed my 73rd birthday, chances I won't be pushing it to the max like you young whippersnappers that are less than 65 or so Also I got a heck of a deal on a Clockwise prop.

Dave

[Papee]

Hey don't forget, I run a hard chined boat. 27mph is tops for me. I don't care for kissing trees or rocks for that matter.

[buster]

Hey Casper,

I just reread your posts and noticed you intend to mount some lights. I just wanted to say it is a mistake to mount headlights on the prop cage. They tend to illuminate the boat, and not much else!

If you want the headlights to illuminate the area ahead of your boat, you need to mount them on the front end of the boat. Just passing on some info I have heard.

Dave

[casper22977]

Buster

thanks for the info. I was going to put them on the cage, but I will put them on the grass rake instead. on another note I got another boat today it is very good shape but it has a 100hp continental dual mag motor on it and I got a small worp prop with it.
need to check out the motor and make sure it runs but I plan to sell it and the prop if you all know any one that might want them.
plans for the boat is a 084 and a redrive, the boat it a 10ftx6.5ft with a rake on the front. It is all stainless riging and cage with a single rear driver seat and a double front.