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1973 Uniflite 31 Sport Sedan with twin 318's

httc10

New member
I am a new poster and hope I have this post in the correct forum.
I have a 1973 Uniflite 31 Sport Sedan with twin Chrysler 318's with Paragon 1.5:1 V-Drives.
If the information that I have been able to locate on the internet is correct, it is as follows:
Weight Dry: 13,500lbs
Fuel Capacity: 2 x 83 gallon tanks, total 166 gallons
So figuring that the loaded weight would be around 16,000 lbs with 4 adults, fuel, fishing equipment, etc.
When using her last year, we were never able to get her on plan. WOT was about 3400 - 3600 RPM and she just wouldn't popup on top.
We new that we would be pulling her out to have fresh bottom paint this year so we just used her at hull speed.
We pulled her out yesterday and the props just look like they have to much pitch. It is hard to read as the one prop is in pretty bad shape and will need to be replaced.
The other prop I can make out is 16 x 15, if it was a cupped prop, then it has worn off.
Does this seem like the right prop for my setup? She acts like she is over propped.
The 318's seem to be running fine and no problem getting well past the 4400 RPM when not under load. We will going through compression checks later next week.
Any help would be greatly appreciated.
Thanks
Danny
 
Let me explain something about twin engine boats: Damn few of them can plane off on one engine--and if the prop on that side is in bad shape, that's what happens.

I have a similar set up (more or less) boat with twin 360s turning 16 x 16 props. For MY boat, with 318s, they used 16 x 14s. Hope that helps.

Jeff

PS: You probably have a lot more "junk" on board that you think! Everyone (ah-hem) does.
 
I do have another question, as I am new to this. I would have thought that if the prop was in that bad of shape that it wouldn't load up.
It is the starboard side and that engine would only get to about 3600 RPM at WOT.
The port would only get to about 3400 RPM.
Both engines not under load will easily go well above these RPMs when not under load.
I have made several calls to several prop shops as well as Michigan Wheel, they all answer really depends on the boat, but most are recommending
either a 15x13 or a 16x14 and eve a 17 if I had the clearance. It is a little confusing.
Is your boat as heavy as mine?
What kind of performance should I be expecting with this setup?
I have seen a couple of other people on the forum that have the same setup and I have sent them a PM to see what are getting as far as performance.
Thanks for replying
Danny
 
I have the same boat with a single 150 gallon tank, she will plane around 3200 maybe depending on load. Trim tabs are crucial to get her out of the hole, I installed 16x15 props last year and it seemed to make a difference. I have to agree with Jeff, amount of fuel, water, people and gear makes a huge difference. I will be honest... In all the years I've owned this boat I've never taken her to WOT...
 
Thanks Matt for responding,
I do have trim tabs, 30", on the boat, but they needed work. I have rebuilt them and I have not had a chance to try them since we worked on them. She is going to be on the hill for several months. We are pulling the motors, getting the bilge area all cleaned up and re-wiring the boat. The previous owners appear not have hooked up the grounding correctly somewhere on the boat as we found that we have a lot of electrolysis on her. So we are doing a lot of work over the next several months.

What speed performance should I expect from her on plane?
What kind of fuel burn per hour are you getting when cruising?

She needs some work, but the hull is like a tank. I plan on having her for a while and we are planning slowly restoring her over the next couple of years.

Any suggestions while we have the engines and trannys out?

Looking forward hearing more from your experiences with her!
 
I cruise at around 15-18 knots and burn between 18-24GPH total depending on load and conditions. I rewired my boat and it has been nice not having to deal with electrical gremlins. I do get jealous of you guys in the colder climates as you get your boat out of the water yearly and can access so many things, here we can boat year round but when I haul the boat out it cost a fortune...

While the motors are out I would do the following.

1- replace stuffing box hoses and clamps
2- replace shaft packing
3- paint bilge under motors and the rest can be done later
4- inspect and replace seacocks if needed


Matt
 
I have a 1973 Uniflite 31 Sport Sedan with twin Chrysler 318's with Paragon 1.5:1 V-Drives.
If the information that I have been able to locate on the internet is correct, it is as follows:
Weight Dry: 13,500lbs
Fuel Capacity: 2 x 83 gallon tanks, total 166 gallons
166 gallons is roughly 1,100 lbs of fuel, which puts you near 14,600 lbs.

So figuring that the loaded weight would be around 16,000 lbs with 4 adults, fuel, fishing equipment, etc.
According to your calculations, there's another 1,400 lbs. being added.

When using her last year, we were never able to get her on plan. WOT was about 3400 - 3600 RPM and she just wouldn't popup on top.
Suggestion:
DO NOT operate your engines while they are not able to reach the specified WOT RPM.
You will risk over-burdening them.


We knew that we would be pulling her out to have fresh bottom paint this year so we just used her at hull speed.
We pulled her out yesterday and the props just look like they have to much pitch. It is hard to read as the one prop is in pretty bad shape and will need to be replaced.
The other prop I can make out is 16 x 15, if it was a cupped prop, then it has worn off.
Does this seem like the right prop for my setup? She acts like she is over propped.
The condition of the engines, the tune of the engines, the hull bottom being clean, etc (relating to prop pitch) will influence your abitliy to reach the WOT RPM.


The 318's seem to be running fine and no problem getting well past the 4400 RPM when not under load.
A no load rpm test is rather meaningless.

We will going through compression checks later next week.
Cylinder pressure checks will help you determine if these are healthy.

Suggestions/questions:

a....... these are 1973 vintage, and if still using the '73 ignition systems, you may want to take a good look at what the progressive spark advance is doing on each engine.
If the ignition distributor's flyweight system is failing to offer the correct progressive and TA, your performance will suffer.
Not may suffer.... it will suffer!

Here's the bad part....... for several years now, the Chrysler guys here have been trying to locate an OEM Chrysler Marine 318/360 ignition advance curve graph. We can find BASE advance all day long... but no OEM Marine specific curve graph.
Unless someone has recently found this info, none exists!
And we certainly do not want to use an automotive curve!

b....... you are pulling these engines, correct? If budget allows, would you consider replacing the 318s with 360s?

c...... GPH is not a means of determining fuel economy unless distance traveled becomes part of the equation.
Perhaps consider installing a fuel flow metering system that syncs with MPH. Now you'd have a much more meaningful fuel burn rate in MPG.

d..... are you loading the boat in a way that may be causing you to be stern heavy? As I'm sure you know, being stern heavy will cause a performance issue.


FYI and FWIW.....
According to many, we have two fuel efficient speeds at which to operate at.

Hull speed and not to exceed.
Planing speed and just a tad bit above.

Anything in between this, is just wasting fuel, and possibly over-burdening our engines.


.
 
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We have a 1972 31 foot sport sedan with 318s turning a pair of 16" diameter by 15" pitch propellers at a top speed of between 40 and 50 mph. The 31' Uniflite weighs about 11,500 lbs. and has no trouble getting on plane. Ours has a single 100 gallon fuel tank.
 

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I have a 1971 31 ft Sport Sedan , it came with the original delivery manual. Props are 16 x 15, my boat has been changed fuel tank wise, I have two 90 gal tanks. Original was 150 one tank. Just about done with starboard engine, failed exhaust manifolds. Great boat!! John
 
The 31 ft sport sedan is a great boat and very quick for its size. We have had ours about 2 years now. I don't have the original manual with ours. We have a black water tank on the port side and a hot water tank on the starboard side. Our fuel tank is in the middle.
 
Here are a couple of pics of mine, wife and I love the boat
 

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Your boat looks beautiful and well kept. Ours has a blue Bimini top.
 

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Rebuilt 220 hours ago under a blue moon which accounts for their color. Mothered over by Mrs. Carter and her four barrels which accounts for the fun, and handled nicely by miss Warner and her velvet drive. Put together with a warm day on the water with good friends, and you can't get the smile off of my face.
 
Reminds me of the Mom with 20 kids who went through 2 husbands--both who died with a smile on their faces!

Jeff
 
We have a 1972 31 foot sport sedan with 318s turning a pair of 16" diameter by 15" pitch propellers at a top speed of between 40 and 50 mph. The 31' Uniflite weighs about 11,500 lbs. and has no trouble getting on plane. Ours has a single 100 gallon fuel tank.

I find those numbers to be remarkable with twin 318's and with the boat weighing in at 11,500 lb.

My SND F/B boat LOA is near 31 foot.
Boat weighs approx 10K.
140 gallon fuel capacity.
80 gallon potable water capacity.
Twin Q/E built 5.7's, approx 280 hp each.... or 560 hp total.
Drives are V/P Duo Props, of which will outperform a pair of single prop drives or shaft drives.

Loaded as usual, 40 mph would be at my WOT.



.
 
The Uniflite 31' hull is clean through the water and designed for speed. I have had mine at 41 miles per hour on GPS at 4000 RPM. I haven't pushed the ladies any harder. You can't even feel her come up on plane even without trim tabs. You just push the throttles to where you want the fuel bills to stabilize. The previous owner claimed 1.5 miles per gallon at 2800 RPM. I love this boat, and have never taken her to WOT.
 
That's great speed an economy for a 31 footer.

My 32 Marinette (360s) gets 1.2 mpg at 19 mph, but it'll only do 32 mph wide open (which I never do--she's an antique).

Jeff
 
Thanks everyone for the information on your boats, I got called away for work and just getting back to this project. Ok so we found out that electrolysis had just about destroyed one of the props, did destroy the trim tabs, bad cutlass bearing and the port engine had a border line compression on one of the cylinders. None of the grounds were wired to the ground plates in hull. I have 2 zero hour rebuilds that we are putting in, correcting all of the wiring, fresh bottom paint, new trim tabs and props. I ran across a CL deal and found 2 Nibral 16x16 cupped (New) so we are going to try these props before having them reworked to see how her performance will be. Shooting for a July re-launch. The rebuilt 318's (we are changing the distributors to the new electronic ignition vs the Chrysler 1st generation ignition, professionally had the Quadrajets tested and rebuilt. So now it is just time to get her all put back together.
 
Don't forget to repack the propeller shaft stuffing boxes as well as the rudder shaft stuffing boxes and any work that is made easier by having the engine bay emptied of motors. Look at your wastewater tanks, your hot water tank, your aft bilge pump, and your fuel cell as these are now much easier to work on. If you can't reach max RPM. the 16 X 16 props might be a little too aggressive in pitch. When your done you will have an excellent boat you can enjoy for years.
 
Well it has been another long day of cleaning the bilge area up prepping for getting it painted. Yes all of the stuffing boxes are getting re-packed. Have pulled all wiring out and checking all hoses. Replacing all of the water lines, a lot of work for weekends, job keeps getting in the way. More to come!
 
When you replace or check the hoses, it's a good idea to double clamp all connection points below the water line, if they are not done already. It will let you sleep better at night, and in Canada it is a requirement of the insurance companies. Don't forget to take a look at the ground wires in the bilge area as well. The connection points get corroded over time. A trick I've learned especially in the bilge area that can be wet, is to crimp on the connector, remove the plastic and solder the connector to the end of the wire. Slide on a couple of pieces of heat shrink on to the wire before you crimp on the connector and shrink them on when your done soldering. Don't forget to put the heat shrink on the wire before the connector gets crimped on. The joint will never come loose and corrosion can never creep in. I didn't install the wires in this picture. Use only rosin core solder. Plumbing solder will damage the wires.
 

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..." Don't forget to put the heat shrink on the wire before the connector gets crimped on."

Ahem, ahem, ahem!

Jeff

PS: That one's in the same league as forgetting to put the plug in.
 
Yeah I replaced my entire bonding system, made a bid difference on how the zincs wear out.nehrn I had my engines out I took the chance to change the stuffing box hoses and clamps, might be a good idea. Toonl, you seem to reach much higher speeds then I thought our boats were capable of. What were your RpMs and and what is your WOT?


matt
 
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