Hswii or someone please help Prop

[carbineone]

Heres my situation.

The boat is a 10 foot GW Invader made of Fiberglass.
Motor is a 1974 Evinrude Lark 50HP.
Its a two seater and all info is based on me at 220lbs and the wife in the boat at 120lbs.
Props are just factory all purpose props I believe.
My drive ratio is 2.66
Prop is a 13x19 aluminum 3 blade.
MPH is from GPS.
Motor has excellent spark that is bright and blue and jumps very well.
Motor has 160lbs in each cylinder and carbs are clean.
Runs great just no RPMs over 4000 pretty much.
Throttle plates open fully.
My manual says 5000 to 6000 RPM range and top HP at 5500RPM

Heres what happened the last time out for a test.Before this last test I had the motor too low I believe as the Cav plate was nearly 1 3/4 inch below the transom and the cav plate was not really visible with the motor that low when running WOT.I now raised it so the cav plate is a inch above the bottom and with the wife driving it is just below the water surface when WOT and thats where it should be right?



With the motor too low it was running 30MPH on GPS at 4400RPMs.I figured with the motor so low it was getting excessive drag and dropping the RPMs.Now this is where it gets strange.I was all excited that the RPMs were going to come up for sure after raising the motor and losing some drag but they actually dropped to 4000 RPMs but the top speed remained the same.

I have tested the tach against a tiny tach and also a inductive auto timing light with the digital RPM readout.I had to do a little math using the inductive timing light but using both the timing light and the tiny tach it appears the tach is reading right on.

When we had the boat out yesterday I thought I would see if the motor is even cabable of running high RPMs so stuck it in neutral and gave it full throttle and the tach would reach around 6000RPM out of gear and stop and go no higher..It does seem that the RPMs are a little slow coming out of the hole.This boat motor combo should be able to run atleast a 21 pithch prop I would think.

We also tried the trim in differant holes and heres how it reacted.On the lowest hole it took off a little faster than the 2nd and third but still the same speed.Went up to the second hole and it was a little slower out of the hole but still really no top speed differance at WOT.Third hole up and it did increase the speed around 2 MPH but then it starts to bouce and chinewalk some so I never even tried the fourth hole but maybe I should but I thought if it was getting squirrley on the third one up there was no sense in trying that.


I have used some of these online prop calculators and they keep saying the numbers I enter are not possible but everyting in my numbers seems correct to me so what may be going on?? Anyway if you need any other info I will add it if you can help maybe.Maybe it is just not capable of doing more than 30MPH with the 50HP but those I have talked to that own these claim is should do 40 plus with the 50...Thanks

 

[steelespike]

Re: Hswii or someone please help Prop

First it is very dangerous to rev the motor beyond about 1500 rpm in neutral.
Reving beyond can result in a runaway and distruction of the power head.
That said the motor shouldn't stop reving unless it has a rev limiter.I don't think a 74 does. I would check the link and sync.Also you might try tickling the choke at speed
if it responds then its running lean.Also check that the stator advances as it should.
Your antivent plate is probably ok but I usually suggest raising to a point just before venting(cavitation)becomes a problem.As far as the prop calculator try increasing the length.a little at a time I'm sure the system doesn't expect a 10' boat with a 50.

 

[hwsiii]

Re: Hswii or someone please help Prop

Carbine, you would have been much better off with a 1974 40 HP Norseman with a 1.75:1 gear ratio with a 10" diameter prop than the 50 HP Lark with a 2.66:1 gear ratio and a 13" diameter prop. You also need to look at everything that Spike said.

Quite frankly I haven't dealt much with very small high HP speed hulls, but I might as well start with yours.

I don't know anything about these hulls, so I need a bunch of pictures of the bottom and the anti vent height above the bottom, I noticed you said that it actually dropped RPM when you raised the motor, but don't worry about that right now.

I also need to know if it has a PAD bottom like a bass boat, it would be right at the transom at the keel, get me some pictures.

Let's start with the prop you are using, it has WAYYYYY too much blade surface area for what you are pushing. You need a 2 blade prop that will get the RPM up and also let us get to a higher pitch prop.

We also need to make sure of where our anti vent plate is in relation to the hull bottom, and that you can do with the following procedure.

6. Anti-ventilation Plate height above keel of boat if it is an outboard in inches, use a straight edge under the keel and sticking out to the anti ventilation plate for a reference
Motor Transom Height

We also need to check the last 3' of the bottom, just take a straight edge and lay it on the bottom both from the transom to the bow and from the starboard side to the port side. In doing this we are looking for areas that are NOT level, see if there are any depressions in that last 3'.

You have to be careful with these type of hulls as they will tend to chine walk at higher speeds, and that can be very dangerous if you do not have the experience required to handle this.

And in order to get the maximum speed you really need to have power trim on the motor, but we will work with what you have.



H

 

[carbineone]

Re: Hswii or someone please help Prop

Thanks.I am going to the library tonight and do some reading on timing and other adjustments..I talked to a guy at a prop place and he did his best to help with 20 minutes on the phone but he kinda came to the conclusion that there has to be something in the motor not being able to run the higher RPMs.He said he is not a mechanic but has been in the prop field for 30 years so he is more likely right.He said he could sell me props all day long but does not think a prop is going to fix the underlying problem and give the performance I am desiring...

The carbs are not adjustable for high speed mixture so I do not know what to think of that..My manual says the high speed is factory set and not adjustable.I have had the carbs apart twice and cleaned them thouroghly..I will try to run it partially choked next time out and see if anything acts differantly...Thanks

 

[carbineone]

Re: Hswii or someone please help Prop

Heres a few pics to start with and let me know if you need more..The bottom has a rib so to speak all along the center and it is 8 inches wide and app. a inch thick..Where do you want the meausurement from,the center rib or off the rest of the bottom so to speak..Someone did mention to me that a 2 blade prop would be best on one of these.

As far as the motor getting changed I believe you may be right that the gearing is off for this particuliar boat but I just cannot financially change it this year but maybe next if we cannot get this to work right..Thanks and let me know anything else you need to know as I am happy to provide it if you can help....Bruce

Oh just to let you know that prop in the pics is a differant one off my brothers 85 HP Evinrude and it is a 17 pitch but in bad shape.My 19 pitch one is nice that I have normally on there...

 

[carbineone]

Re: Hswii or someone please help Prop

If I run a straight edge right off the center rib the antiventilation plate is 1 1/4 inch above that and only around 1/2 inch higher than the part next to to the rib that makes up the rest of the keel...

 

[carbineone]

Re: Hswii or someone please help Prop

HSwii.I started a new thread on this subject of Sparkplugs over in the Evinrude section but thought I would put it here too in case you do not see the other thread.I was looking at my sparplugs today and someone had Champion UL77V,s in there and from reading here they should be either

L77JC4,s or QL77JC4,s I went with the Q ones as I read a deal from Champion that says the Q ones should be used in the OMC CDI ignition systems or they can cause some sort of interference with the electrical system and cause the motor to run incorrectly..It is a longshot but maybe the wrong plugs in there was starving the motor of performance in some way or maybe throwing off my tach meausurements through interference..Just a theory and hoping maybe the motor will have undergone some miraculous changes due to the wrong plugs being in there.Never know...Thanks

 

[hwsiii]

Re: Hswii or someone please help Prop

carbine, take it for a run and let us know what it is doing with the new plugs. And we will go from there.



h

 

[steelespike]

Re: Hswii or someone please help Prop

As far as the hs jets they can be replaced if a change is in order.

 

[carbineone]

Re: Hswii or someone please help Prop

HSwii,gained maybe a little RPM with the new plugs but nothing astounding.Anyway after seeing the photos any ideas what to do?I have been looking at some two blade props but they are few and far between..

Also any theory on what I asked earlier as to why the RPMs dropped when I raised the motor up? Thanks

 

[steelespike]

Re: Hswii or someone please help Prop

As far as the motor height if your not getting venting problems you could raise it more.Won't give you enough rpm to solve your rpm drop.Have you checked the things I suggested?
Have you checked that the carb throttle plate is opening all the way?Is the throttle cable binding or out of adjustment?Is the stator advancing with the throttle.
I believe there is also a device that limits the throttle in neutral; and reverse.
If it is damaged or out of adjustment it could restrict the throttle.

 

[Frank Acampora]

Re: Hswii or someone please help Prop

Here's a 10 footer with a weaker 50 than your Rude. It goes about 44. Before I got it set up properly, it only went about 35. I needed to add 2 inches of height to the transom, and still needed to raise the engine another two inches more for a total lift of four inches. Now, while my cub is a tunnel hull, and not directly comparable to your GW, the principals should remain relatively similar. You are probably running a 50 on a hull that was originally designed for a 20 or 25. The hull is extremely stern heavy and it will not take advantage of the riding pad (8 inches wide) in the center. The engine will thus be sitting way too low and even in mid range height adjustment will not act as you would think. I suspect that you have mounted the battery and gas tank in the stern compartment. Moving both forward will help.

I would be willing to bet that if you took a photo at speed, it would show too much hull in the water. The trick is to maximise weight distribution and engine performance to get the hull riding as high as possible. Unfortunately, it is not possible to move seating position, but get as much weight as possible out of the stern.

I recommend that FIRST: Get rid of the old banged-up prop. Sorry--change your existing prop. It has way too much area. Try to find one with less diameter and equal or more pitch. Two blade would be nice if you can find one.

Second: Raise the engine an inch at a time until she "gurgles" on the edge of ventilation on the straight.

Third: Be extremely careful. These small overpowered hulls will turn around and bite you in the **s in a New York second with the slightest driver error. I have flipped mine on three occasions.

I would also recommend filling the stern compartment with foam blocks or empty 1/2 gallon jugs. With that engine, that hull will likely be only neutrally bouyant if flipped or immersed and the extra flotation will make salvage easier.

Also, If you don't have one now, do not run the boat again until you have installed a "Dead-Man's" or "Man Overboard" kill switch. Beats the hell out of having your own prop cut you.

I have also included a photo of a 14 foot flat bottom very similar to your GW with a 125 for power. It goes 60. However, I am using a stainless "cleaver" prop to maximise potential. Props are important and critical for gaining maximum speed available. The weak 50 has a two blade Michigan "AJC" type bronze prop, cupped all the way. You need to search around to find racing type props that will fit your engine.

 

[carbineone]

Re: Hswii or someone please help Prop

First I will address Steelspikes comments.Yes I checked that the throttle plates are opening fully as suggested here by another member and also checked the timing advance and all is doing as expected..As far as the throttle it is set up with a simple older style dual stick..One for throttle and one for gears..I did get the original single stick one with it but it was not working properly and I prefer the dual setups anyway as they are much simpler and less complicated..Could there possibly be something in using the older dual setup as opposed to the original single stick control..I doubt it but who knows..

Frank,my battery and fuel tank are already moved to the bow,I am almost thinking we may have too much weight to the front and the front hull is just plowing too much..Any possibility of that?When I watched the motor in the water at WOT with wife driving the anti vent plate was just visible under the water line and thats the way I understand it should be from reading here..

I already have foam in the rear on both sides that was there from the factory I believe.I am looking into the deadman and that has been suggested to me before.I am thinking one from a jet ski type might work.As far as the prop thats just a old one I had on there that I robbed off my brothers old junk boat to try some differant pitches.It a 13x17 but the one that came with the motor is a 13x19 and in very good shape.I will show a pic of the 13x19 but theres really no performance differance between either one..

I have been looking on Ebay and as stated two blade ones are very hard to find but I have been looking at some smaller diameter ones with 3 blades but with smaller blades too..I reallly cannot afford to buy 10 props to see which is going to work best so may take a chance on one in the smaller diameter range with narrower blades maybe...

Will a smaller lighter 3 blade prop with less blade area likely produce more RPM and speed or not? Thanks

 

[Frank Acampora]

Re: Hswii or someone please help Prop

It is possible that you do have too much weight in the bow. As I said, you must experiment with weight distribution to get the best balance. USUALLY, moving weight aft in a hull works to get the bow up--think of a Jersey Skiff. However, these little hulls are different, more critical, and not necessarily set up the same.

Notice how my weight is about midway back on the 14 footer. Gas tank (15 gal) is located just at the splashwell. She rides solid with the current balance but you can see how little hull is on the water. Too much weight in the stern of this boat would possibly cause porpoising and possibly contribute to a blowover. (In early stages of experimenting, this hull DID porpoise and chine walk)

Look again at both photos I attached. Note how both hulls are set up to ride on the last 18 inches of running surface. The little Cub does not have power trim, and I actually need to lean over the steering wheel to drop the bow and get it onto plane. I can actually feel a difference in speed by shifting forward or backward in the seat.

No matter where you see the cavitation plate, you still need to raise the engine until it is just on the edge of ventilation on the straightaway. That is the way to maximum performance. --A cupped prop is almost a MUST as it has more "bite" and allows higher engine settings before ventilation and cavitation sets in.

Just remember: Only change ONE variable at a time, check the results, and apply logic to the next change. For example: since it is easy to do, Move the fuel tank backward and see if performance improves. If it does, then consider moving the battery. If it does not improve, move it back and try a different change. See: It is little steps at a time that add up to final performance gains. (The longest journey begins with the first step, grasshopper)

 

[hwsiii]

Re: Hswii or someone please help Prop

Carbine,

Let's start with the prop you are using, it has WAYYYYY too much blade surface area for what you are pushing. You need a 2 blade prop that will get the RPM up and also let us get to a higher pitch prop.

Frank

I recommend that FIRST: Get rid of the old banged-up prop. Sorry--change your existing prop. It has way too much area. Try to find one with less diameter and equal or more pitch. Two blade would be nice if you can find one.

I have great respect for anything that Frank says, as I have seen a great many of his posts that are right and directly to the point of the problem. In my opinion, he is right as well in this case. We agree on many of the same problems and how to cure them on your boat. If I were you I would listen to what he says, as I can guarantee you that he knows more about this particular topic than I do.



H

 

[carbineone]

Re: Hswii or someone please help Prop

Thanks fellas and will do the experimenting you are telling us..Going to try the weight redistribution thing first and take a chance on prop I think may fit your description also..It will be later this weekend probably as the dang weather stinks as usual in Nebraska..Only 52 degree high today and only 45 by wendesday.Sick of it already....

On the prop do you think a smaller diameter 3 blade with quite a bit of cup in maybe in a 21 pitch or so might be a starting point?Its easy enough to redo the weight distribution and that costs nothing but the prop changeouts are a differant story....

Disclaimer:I understand any advice on props given here to me is my sole responsibility and any suggestions made here are not in any way any member heres fault in not correct.LOL

 

[carbineone]

Re: Hswii or someone please help Prop

Update on the low speed..We finally after a week and a half of miserable weather got a chance to get the little Invader back out.I mentioned earlier we tried to run this on the third hole up on the tilt but it seemed to want to get squirrley and chinewalk but the kid was driving it then and I was the passenger so never let him push it then.Today I drove it and trimmed up to the third hole the RPMS came up drastically to around 5100 and it goes a whole lot faster.I forgot the GPS today but will take it next time out but it sure increased the top end speed to 40 for sure up on the third hole.It was a night and day differance getting the motor tilted up a little further.I was just worried when we moved it to the third hole last time out but it is doing what the boat should now.This is with the 17 pitch prop.It was not unstable at all as I first thought but we were just not used to what the boat was intended to act like when running properly...The bow was just sitting way too low and dragging in the water as I believe I and someone else mentioned here..

It does what people say it should that I have heard from others who own them and from videos I have viewed of them on the water.It will jump waves and actually leave the water now and thats what they are supposed to do if you wish them too..I myself though at my age am going to stay with calmer waters and leave the jumping to the young fellas on the Jetskis,well maybe every now then..Anyway I believe we are getting real close to getting the performance we should be getting out of this with the 50HP..Am still going to mess with the props a little and hopefully find one that will give a little more RPM and good performance all around..The 17 pitch is my brothers anyway and its dinged up and has broken pieces and such...I will update the speed numbers on GPS when we get them next week and see what you think....Thanks

 

[steelespike]

Re: Hswii or someone please help Prop

It appears you are being careful.I just wanted to mention that as you start getting the speed up A fast boat can catch a wave and go out of control very quickly sometimes it could rarely jump a wave and dive into another suddenly stopping with serious injuries.Just be careful and have fun."Wear" your pfd's.

 

[carbineone]

Re: Hswii or someone please help Prop

Thanks Steelspike,no I do not intend to put myself and especially my son in danger by being careless over a boat.I am a pretty wise OLD fella and have learned alot over the years that getting injured hurts,the boat seems to handle waves pretty darn good though but we will be careful of course..

Anyone have any ideas what kind of power tilt setups might have been available for these 1974 50HPs and where a guy might look to find one.It would be nice to have the tilt as mentioned here by Hswii I believe...Thanks

 

[carbineone]

Re: Hswii or someone please help Prop

Well we had the GW out today with the GPS and I was a little overzealus on the speed increase.Never made it to 40MPH but 36MPH.Still a pretty significant increase though over the 30MPH.Now I was looking at some props here on I Boats and they have a cupped 3 blade ones but it says if you use a cupped prop you need to drop the pitch two sizes from what your prop is that you are replacing.For example the 17 pitch I used for testing would become a 15 pitch in the cupped ones? Why the change in pitch from standard to cupped? I may just start a new thread on the cupped props too as this one is mostly concerning other problems...Thanks