Ventilation 65hp chrysler

[Texasmark]

Hmmmm. I guess that's another advantage to Merc coming out with the thru prop exhaust.....leaves you a spot to put a trim tab!

 

[Sea Rider]

Ias,

If plan building a new doel fin (pressure plate) try same but without vertical sides, just flat horizontal.The horizontal fin is what makes combo to plane faster. Trim OB at 90? for combo and anticav plate to ride parallel to water level, deck weight must be well aft-bow balanced. Do you plan to install a standard or a induction tach to check max wot rpm achieved as usually loaded, or you can live without knowing ?

OB revving happily at max wot range along a prop maximization could make the combo to perform much better than at present. Being a non thru hub prop could be difficult to find and dial a proper pitch size for that to happen.

Happy Boating

 

[las]

The idea behind the vertical sides was stolen from other designs I saw and looking at the bennet sport tabs. They claim to achieve +30% lift with vertical fins on their design.
And the theory seems sound, water is held in under somewhat higher pressure thus generating more lift. I also think that the denser water would help the top blade a bit!

But it is definitely a subject I would love to hear and discuss more about, because my 2mm stainless steel plate arrived today. I'm about to make the tabs and was planning on doing something similar to the tabs.
I have about 8 inches of available space on either side of the transom, and the plate I bought just happens to make it possible to make two tabs 8" x 10" (with vertical sides

I just ordered one of those square Chinese tach's on ebay, I have to know where I am RPM wise, otherwise I can't play with the prop later, although their hard to find these days.

 

[Texasmark]

Michigan Wheel! I got a 3 blade (bronze or brass, don't remember, but it was yellow) MW prop for my new 25 hp Wizard (sold by Western Auto auto parts stores) in 1958 so I could pull a person on water skis. No body else had one.

 

[las]

No Title

Tabs fabricated and installed, and what a huge difference it makes!

Made the tabs around 8x10 inches with vertical fins and I think it turned out pretty good.

Me and the boy took her out for a test and even fully retracted the boat would just glide onto plane with the engine tucked all in.
Before we had to climp the hill and you would know when on plane, this time I was like "I think were on plane now?" and was going 16 knots....

Well actually they are not fully mounted yet, stil need to connect the wiring harness. But we did play a little with the trim by simply connecting the appropriate wires to the positive on the engines wiring harness.

Now I just need to fabricate a switch holder for two (on)off(on) switches.

The hinges was the toughest part, I found it hard to find a quality I would trust. I ended up with 2mm thickness stainless steel hinges and would think that should do it!

 

[Texasmark]

Nice job. Glad it's working for you. Thanks for the update.

 

[las]

I finally made my tachometer work! Not an easy task when you have an old Chrysler 20 stator pole outboard and a 10 or 12 pole Faria gauge.
I managed to find a 2 to 1 AC square wave divider in Germany and it actually worked.... (bought a backup induction one from China)

Yesterday we went sailing again, now with everything working, trim tabs, engine trim and tachometer, we were "only" able to hit 28 knots at 5500 rpm with two adults and two kids.
Just couldn't make it go faster regardless of what I tried with the trim.

The prop is 10x17 and gear ratio is around 1.6. Now as far as google can tell that puts the prop slip at almost 40 percent! I'd say that's a lot.
Are we still talking rough bottom, and / or bad prop?

And what slip percentage should I expect once the remaining issues have been solved?

 

[jimmbo]

Or a lot of ventilation
What rpm is your tach reading? Is it accurate?

 

[las]

I can't verify the rpm before the china one arrives, but it felt right and showed 5500 at wot.

Also didn't feel like ventilation like the earlier experience! But it might be?

 

[jimmbo]

5% - 10% slippage is the average. Running the numbers for a 17 prop with 10% slippage shows 43 knots or 49 mph. 17 sounds awfully big for a 65 hp with a 1.6:1 gearing. A 12 inch at 5500 and 10% slip shows 30 knots, or 35 mph

 

[las]

No Title

hmmm, it could be a 12 inch.

Have a look and see what you make of it.

 

[jimmbo]

Have you taken the prop off and looked for any other numbers?

 

[las]

yes and I didn't find any, perhaps I could try again.

According to what I've read in the Chrysler forum the first series of numbers is a part number, the second is the pitch!
This model lower leg all used 10,? inch diameter props, hence no need for the diameter written on the prop.
The "pitch" number is of course very hard to read but earlier I was sure it said 17, and I still think so. The number 2 would not have that sharp angle in the upper right corner, I think.
Also from the pictures wouldn't you think it was rather wide / deep for a 12 inch?

 

[las]

Look at that last digit! And then look at the last digit in the first series 493...

Now I actually think it's a 13 inch pitch...... Then things make a little more sense, slip is still on the high side though, but nowhere near 40 percent.

 

[Texasmark]

5% - 10% slippage is the average. Running the numbers for a 17 prop with 10% slippage shows 43 knots or 49 mph. 17 sounds awfully big for a 65 hp with a 1.6:1 gearing. A 12 inch at 5500 and 10% slip shows 30 knots, or 35 mph

When I snapped the picture in my Avatar, my specs were:

Gearbox: 2.3
Prop: 24 XL Ballistic SS
RPM: 5700
Screw in wood: 56
GPS actual: 48
Slip:14%

Considering what you see and what Normal wakes look like, I don't know where you get your 5-10% slip average numbers.

 

[jimmbo]

Maybe I run better engineered propellers that are able to make better use of the HP.

 

[jimmbo]

Look at that last digit! And then look at the last digit in the first series 493...

Now I actually think it's a 13 inch pitch...... Then things make a little more sense, slip is still on the high side though, but nowhere near 40 percent.

You say the gearing is 1.6:1. That does seem like tall gearing for a small motor. Do the props look like they are 10 inches in diameter? Even 20 hp engines swing larger props. Ok I will admit in the 1960 OMC had some weird gearcases on their V4s 60, 65,75,80, 85, and 90hp engine that spin 10 in prop and they used a 1.15:1 gear ratio. OMC went modern in 1969 and switched much lower gearing, around or close to 2:1 in the v4s and 29:12 in the 3 cylinders.

There are no numbers on the ends of the hub?

The numbers you are looking referring to, look to me, like numbers a rebuilder would stamp on

 

[Texasmark]

Maybe I run better engineered propellers that are able to make better use of the HP.

Maybe so. Ballistic is an off the shelf prop, no fancy custom tuning. So if I'm not slipping, I am loading the engine which pulls the rpms down so it's a crap shoot, less slip and less rpm hopefully for more speed. But that's a crap shoot till you do it.

 

[Texasmark]

You say the gearing is 1.6:1. That does seem like tall gearing for a small motor.

'94 Mariner sales brochure: Both 50 and 60 hp, small gearcase, 10" prop dia range, 1.64 gearbox; 75 and 90 13" prop dia range, 2.33 gearbox.

 

[jimmbo]

'94 Mariner sales brochure: Both 50 and 60 hp, small gearcase, 10" prop dia range, 1.64 gearbox; 75 and 90 13" prop dia range, 2.33 gearbox.

This is a Chrysler engine, 65 hp.