16ft Glasspar w/65hp 2 stroke

[RRafkin72]

I've got a new to me, 1960 Glasspar Citation, that I'll be putting a 1969 Mercury 65hp 2 stroke on. I have acquired the hull, engine, and lower all separately and do not have a prop yet.

I'm curious if anyone has a similar vessel and power plant that could spare their 2 cents on where to start as far as pitch and diameter?

 

[Willyclay]

My Dad had a 1960 Glasspar Avalon which I used many years after he passed. I mounted a Mark 75 on it that had a two-blade, bronze prop. No clue on the prop specs. The link below should get you to the Mercury Propeller Selection Guide. That should help you narrow your choices. Good luck with that great old boat & motor!

Prop Selector: Find the One for your Boat | Mercury Marine

www.mercurymarine.com

 

[Willyclay]

I had no luck getting any response from the Mercury Marine link I provided so started looking elsewhere. Found Boat House Bulletins by Mercury from 1969 which were actual tests of their motors on different boats. There were six using a single MERC 650EL on them ranging from 14.5 to 17 feet, all fiberglass but not a Glasspar. Five of the six tests used the same prop, A-48-37900A2, which I believe specs-out at 12.5 inch diameter & 15 inch pitch. The smallest boat used 17 inch pitch which is understandable. Hope this helps. FYI, beware of used props that may have a spun rubber hub due to aging although they can probably be repaired. Good luck!

 

[Texasmark]

Prop shops can and will loan you a prop for testing with the requirements that you return it, if not the right answer, with it in the same condition in which it left their shop.....so they can sell it as new to another customer.

If you want to start with the prop listed in the tests you retrieved you can purchase one here: https://www.southcentraloutboards.c...r-40-50-60-65-70-75-80-85-90-100+hp-42469-prp

With that said you need a starting point and if I were doing as you are, this would be a good place to start. For 120 bucks in todays market it's worth a try. Your performance needs to be monitored to see if you made the right selection. Performance characters start with a tachometer and recording the engine RPM with the throttle firewalled, boat on plane with power trim set for max speed, or if no PTT, adjusting the tilt lever on the engines transom bracket to a notch that will give you the best speed with your max anticipated load in the boat. If the Glasspar isn't loaded with water logged foam, you should have a good performing hull...those are fine boats and plane out easily besides having the hull designed for reasonably comfortable ride in a good chop.

Then you need to obtain the full throttle operating range of your engine. It will be somewhere around 4500 to 6000 RPM. The results of your initial testing as I described should put you above the mid point in your RPM range which will allow you to increase revs. under lightly loaded boat conditions yet remain within the recommended range. 2 strokers get their power in RPMs since they are usually low in cubic inches. Since cubes produce torque and HP is torque x RPM essentially, you need to keep the RPMs up to keep from burning pistons and other detrimental things low RPMs at fire wall throttle conditions cause.

Faztbullet is an excellent source for info on here and has helped a lot of folks. He probably has an old shop manual that lists the recommended RPM range for that engine if you don't have another source.

If you plan on water toys being your main boating enjoyment you will need to prop with less pitch to keep the RPMs up as stated under those conditions. If you prop for such performance, you need to keep the throttle cut back under lightly loaded conditions to stay within the engine's recommend operating range.

Good luck!

 

[RRafkin72]

Thanks a bunch guys, sorry for going quiet I've been under the weather lately. I do understand that I need a starting point. Currently mid motor swap from a 50hp to the 65hp so I will likely start with the 12.5 x 15 and get her running first. Then do some sea trials and log some numbers! Once she's runnin right and I have a little bit of fun, she's getting torn down and restored from the stringers up.

 

[jimmbo]

The 4 cylinder 65 uses a larger gearcase than the 50hp or later 3 cylinder 65hp. I believe the Gear Ratio is 2.33:1, and with that a 13 - 13 1/2 X 15 would be a good starting point

 

[RRafkin72]

The 4 cylinder 65 uses a larger gearcase than the 50hp or later 3 cylinder 65hp. I believe the Gear Ratio is 2.33:1, and with that a 13 - 13 1/2 X 15 would be a good starting point

How about number of blades?
I've seen some older units with 2 blade props
A lot of em with 3 blade
And I'm seeing newer stuff with 4 blades

And does material affect performance or just longevity?

 

[racerone]

Do an inspection and evaluation of the 4 cylinder 65 HP before spending any beer tokens for a prop.

 

[RRafkin72]

Sound advice, could use a cold one right now. I'm waiting on a few seals to show up and I can then mate the lower to the engine. I've got my current engine completely disconnected and ready to pull. Once I swap then it looks like just cleaning up some wiring and hopefully ready to go.

 

[jimmbo]

How about number of blades?
I've seen some older units with 2 blade props
A lot of em with 3 blade
And I'm seeing newer stuff with 4 blades

And does material affect performance or just longevity?

The fewer the Blades the less Drag and thus more speed, however more blade area, gives a better bite on the water, and more blades tend to run smoother. Personally, I will Never run more than 3 blades, and if I could get a Modern 2 blade for my I/O, I would do so in a Heartbeat.

 

[Thirsty Endgrain]

Nice glasspar. I have a '64 Seafair Sedan that just matured into a pilothouse.

I was gonna say to make sure the boat itself is sound but then read that you are gonna tear into her. I believe the '60 had wooden stringers unfortunately, so that'll add a fair bit of work.

Mine is 17' and powered by a 4 stroke 90hp with a 4 blade 13.5 x 15p. So much different in all regards and not helpful for your situation.

Hope you got a title for that thing? Last reg in '11 has me asking.

Good luck and document the rebuild!

 

[jimmbo]

And does material affect performance or just longevity?

I forgot to comment on that part

Material will certainly affect Performance. Bronze, Steel, Stainless Steel, permit thinner Blades, which are more efficient than those made of Aluminium. They also enable the Prop Engineers to design Blade Geometry that is also better.
There is a Price, and not just in money. An Aluminium Prop is kind of a Sacrificial Lamb on Impacts. It will bend and/or break before other parts of the Driveline are seriously damaged. Stainless, on the other hand being stronger, doesn't break/bend as easily, and passes the Impact Shock on to the Driveline. I have bent a few Propshafts when using Stainless Props, and it gets expensive, as they should be replaced, as they really can't be properly/completely straightened.

 

[RRafkin72]

 

[RRafkin72]

Really excited I got her out on the water this weekend finally. Previously I had one failed sea trial attempt, splashed the boat fired her up and she would die once in gear. Took her home went thru the carbs and got her running better, adjusted some things as far as idle and carb pickups, also solved my reverse lock issue and so this weekend was the first real sea trial and it couldn't have been a better day.

I currently have a tach hooked up but I believe it reads because it was about 300 above my timing light/digital tach. So I'm shooting in the dark a bit still until I sort that out. But during sea trial I saw about 6500 rpm at full throttle on my helm tach which reads high. I went with a 13.25" Dia. × 17 pitch prop for a starting point. The boat was light and unfortunately I don't have numbers in speed over ground yet, but it felt like we were moving pretty good. I had the trim set to the 3rd hole up and I think I'll go one more next time and load the boat a little more to see how she rides.

I'm curious if anyone has Intel on what a 1969 merc 650s max rpm should be?

Can't thank everyone enough for all the advice so far. I'm going to be doing more tuning and testing soon!

 

[Texasmark]

How about number of blades?
I've seen some older units with 2 blade props
A lot of em with 3 blade
And I'm seeing newer stuff with 4 blades

And does material affect performance or just longevity?

Per some Merc data I stumbled across years ago, the fewer the blades the more efficient the prop as it has more "clear water" hitting the blades. However, blade area is what contacts the water and if you need a lot of whoopie you need a lot of blade area.

Merc ran 2 blade props OEM back in the 50's and it wasn't until they went to Phantom Black paint on their 100 hp Merc 1000 did they show a 3 blade as OEM......per my dismal recollection.....Apparently they saw the 100 pushing larger boats and that meant more blade area.

One of the differences in 3 and 4 blade SS (in particular) is the design of the prop. 3 blades have high rake (blades bent back from the root) which gives good bow lift, getting the hull out of the water and increasing speed. 4 blades are just the opposite where they are designed to push heavy loads and get the stern up, be it a larger boat or pulling water toys.

Solace has a tutorial on their designing of their 3 and 4 blade props which you might find helpful. I have a Solace 4 blade SS that I bought for cruising just over planing speed and the shallower pitch and extra blade help me to maintain a constant speed rather than too fast one minute then a correction and too slow the next needing another correction.....again per my dismal recollection.

 

[jimmbo]

A 1969 650 would have a WOT Rpm range of 4800 - 5300.
I find 6500 with a 17" prop on your boat a little high, either you have a lot of Slippage, or the Tach is way off.

As mentioned, Mercury did offer a lot of 2 Blade Props for their Engines in the 60s. The 2 Blade Props had a larger Diameter, more Blade Area per Blade, and different Rake Lines, than the 3 Blade Props of the same Pitch. If you could find a Quicksilver Accessory Catalog from the late 60s, 70, 71, or 72, the specs would be there. I recall one of the "Man Magazines"(Pop Science, Mexchanix Illistrated, Popular Mechanics), doing a bunch of Prop Test Comparisons on a Merc Motor, and it had 2 and 3 Blade in it. The Testing revealed how the # of Blades, along with the Blade Area and Dia affected the Acceleration and Top Speed.
Personally, I wish Mercury still offered 2 Blade Props, I would have one on my Boat so fast, you would miss the swap if you blinked

 

[racerone]

I think 2 blade props will allow revs / power to build up quicker.

 

[RRafkin72]

4800-5300 thank you Jimbo! I have a photo tach that I will use to compare the helm tach and the timing light tach next. Hopefully I can make some sense of things. I read on a tag on the the engine mercury wants you to use only a quicksilver tach with lightning energizer ignition, anyone know anything about that?

 

[jimmbo]

Compatibility, as well as a Sale.
In the late 60s early 70s Merc moved from using the Ignition System for the Tach Signal, to the Alternator. For me, I find setting the Tach for # of Cylinders far Easier, than for an Alternator, as I can count Cylinders.

 

[RRafkin72]

Compatibility, as well as a Sale.
In the late 60s early 70s Merc moved from using the Ignition System for the Tach Signal, to the Alternator. For me, I find setting the Tach for # of Cylinders far Easier, than for an Alternator, as I can count Cylinders.

OK so I have currently a random aftermarket tach that came from some automotive project I've done. I believe I tried to wire it to to the signal of the ignition and remember not having any luck, so then I wired it to the rectifier that goes back to the Alternator signal and it came alive. But I'm wondering if I maybe need to go back to the ign signal to get a correct read out