What props should a 1979 Trojan Cruiser have?

[erikgreen]

My friend has a 1979 Trojan F30 Sport Cruiser 304-305. We suspect the props are wrong (they were replaced following a grounding).

Can anyone tell me what props are supposed to be on this boat from the manufacturer?

It's the dual engine version, twin chrysler 318s @225HP each, 8100 lbs.

Current max speed is about 21 kts at 3000RPM.

Erik

 

[steelespike]

Re: What props should a 1979 Trojan Cruiser have?

Not an expert and don't know the specs for your motors but I'll try to get us started.It appears you are at least about 1,500 rpm low.Thats alot to make up with just the props.Something like 7 inches.The guys here may be able to come up with some idea of a typical setup.If we knew the demensions of your props we could most likely come up with some suggestions.And be able to tell if something else is going on.
You could check the compression on the engines. and be sure the throttles are opening all the way.Also is the bottom clean?

 

[rndn]

Re: What props should a 1979 Trojan Cruiser have?

What props are on there now?

 

[Bondo]

Re: What props should a 1979 Trojan Cruiser have?

Erik,.......

That Big Cruiser is Just like every other boat when it comes to Propping it,.......

Without knowing exactly What's on it Now,+ the #s the driveline is pulling,......
There's No Way of knowing what the Answer to your Question is.........

If the WOT of those Chrysler's is 3000rpms,....... Is that Both motors,..??.....

Are the motors making the Power they should be,..??...

Is the Bottom of the boat 3" Thick with Creatures,..??.....Maybe it's already got the Right props,......
A Dirty Bottom will create the same Issues.......

 

[erikgreen]

Re: What props should a 1979 Trojan Cruiser have?

According to what we know, WOT should be about 3300 or so.

The engines were rebuilt 2 and 3 years ago (port and starboard) including the carbs.

We've checked to make sure the throttles open all the way and that the back barrels on the carbs open up.

The engines can make close to 4000 rpm at the dock without a load.

The props were replaced less than 2 years ago after a grounding. We suspect that the props aren't right, hence the question... we don't know what the current ones are labeled, what they actually are (may be different) or what the manufacturer originally recommended.

We're looking at pulling the props and taking them to a shop to get the actual pitch measured... we want to compare this with manufacturer's spec + with what the shop that repaired her after the grounding thinks they put on.

Erik

PS: Forgot to mention... it's a freshwater boat, no marine growth of any kind. Bottom is ablative paint, and is reasonably smooth for its age.

 

[erikgreen]

Re: What props should a 1979 Trojan Cruiser have?

Here's some new information.

We pulled the props off the boat, and they're 14 inch props with 11 inch pitch, 4 blades each.

Can anyone tell me whether this is the same as the original pitch supplied with this boat?

I can supply more info as needed, if I haven't hit any questions you might have above. We really need to figure this out before next season if we can.

Erik

 

[steelespike]

Re: What props should a 1979 Trojan Cruiser have?

I haven't been involved with twin straight inboards but 14 X 11 props on a
8000lb twin set up seems it should turn more rpm.My vintage 4,000lb 125 hp
inboard was slightly over propped and would turn close to 3,000 rpm with a 14 X 14 prop.Speed was rated at over 31 at 3,200.Hp was rated at 3,200 rpm.
It's not a good idea to rev the motors in neutral.They should rev to distruction speeds unless they are governed.Pretty sure the 318 is rated between 4,000 and 5,000.Unless I'm missing something I would think wot would be around 4,000 to 4,500.Perhaps 3,300 is the most efficient speed and it is governed to run there.

 

[erikgreen]

Re: What props should a 1979 Trojan Cruiser have?

Would there be a mechanical governor somewhere?

My friend who owns the boat remembers driving it at 30 kts or so when he got it, prior to the prop replacement. His memory may be faulty on the numbers by a couple knots, but it did formerly go a lot faster.

Erik

 

[steelespike]

Re: What props should a 1979 Trojan Cruiser have?

Would there be a mechanical governor somewhere?

My friend who owns the boat remembers driving it at 30 kts or so when he got it, prior to the prop replacement. His memory may be faulty on the numbers by a couple knots, but it did formerly go a lot faster.

Erik

I'm a little puzzled By your statement of 4,000 rpm in neutral.If the motors
won't exceed 4,000 then something is up.It is unusual for both to respond the same if there was some sort of mechanical problem.You need to check for a govenor.There certainly could be one.I would guess that on that old of a setup there would be some sort of extra lickage on the carbs that would override the throttle. But there could be some sort of internal device as well.
As I understand it 4 blade props are generally to improve low end performance or for heavy boats/loads.While your boat is heavy 450 hp shouldn't be challenged trying to push it.4 blade props will tend to lower rpm a little (100 to 200 rpm)when compared to a similar 3 blade prop.
While your at it do a compression check on the motors.
I would think these motors would run about 4,500 rpm at WOT.

 

[erikgreen]

Re: What props should a 1979 Trojan Cruiser have?

We'll take a look for a governor, but since we've been working on the carbs all last summer I kind of doubt there's one there. We even bought the manual for the carb and a book on rebuilding it in case that would help.

4000 rpm may have been lower than the upper limit... it's probably as far as the mechanic wanted to go at the dock.

On the water, with those props, the boat only turns about 3100 rpm max. To my mind if the props were pitched too low, we'd get up to 4000rpm plus but not get as much speed as we could. On the other hand, overpitched props would mean we'd get the rpm we're seeing and the lack of speed too.... but could an 11 pitch prop be too much for a boat this size?

It's almost like we can't get the boat fully on plane... but there's no water standing in the hull, no foam to absorb it... there are benches in the rear of the boat for scuba tanks, but I don't see them weighing more than 300 or so pounds.

Suggestions welcome, as well as any pointers to trojan manuals showing the original factory prop pitch.

Erik

 

[steelespike]

Re: What props should a 1979 Trojan Cruiser have?

Again keeping in mind I'm working with just a basic knowledge of props.
In my mind 11" pitch is for an application in a boat difficult to push ie:a pontoon.In my opinion the 4 blade 11" pitch would be on a 8,000 lb single screw boat.Possibly a boat with a displacement like hull difficult to plane.
You may want to pick a brain at a well established cruiser dealer.Or maybe the Michigan wheel prop site.

 

[erikgreen]

Re: What props should a 1979 Trojan Cruiser have?

Okay, I just got a summary email from my friend (the owner) and here it is for more information. I've also submitted a request for prop sizing to michigan wheel, so we'll see what they say.

Here's the email from my friend:

The engines will reach 4000 rpm WTO (Wide Open Throttle) at neutral. Doing the math
the engines should be able to drive the props to 41.66 mph (assuming no load etc.)
The owners guide shows max speed at 4000 rpm at 34 mph. Its understandable to me to
see 7 mph drop due to boat weight (~9000lbs) and hull resistance , that make scene.

FYI: 1979 Trojan F-30 Model 304
w/twin 225 Chrysler (LM318B)
Carter carburetor: AFB 9263S
electronic ignition distributor (replaced original points distributor)
Borg Warner 1:1 transmission (no V-drive)
Fuel water separator for each engine
One of the two fuel tanks (rear) has an one way valve to reverse fuel flow.

Here is the problem...
When I bought the boat we tested the boat at over 31 mph with 5 people on board, rpm
around 3500. With a heavy load 20 mph was normal.

Currently under a no load the best I can do is 28 mph, with a normal load (4-5
people w/o gear) 20 mph and with a heavy (scuba) load 11-14 mph. The engines will
normally provide 2200 to 2500 rpm and seem to be very load sensitive, a moderate
wave will drop speed by 2-5 mph. If one engine stalls (which happens a lot) the
other engine drop rpm significantly. Rapid throttle advances will cause the engine
to stumble or backfire.

OK what does that tell us... the engines can provide the rpm and the props are an
appropriate pitch to match the specs. But the engines can spin the props to spec rpm
when under load. I'm opinion this is a power delivery or torque problem not an rpm
issue.

So here is the question...
What can prevent an engine from performing while under a load?


Here is what has been done...
Both engines, carburetor and transmissions were rebuilt (due to oil leaks).
The problem seem to start after the first engine and carburetor was
rebuilt. Sent carburetor back to rebuild and had it checked (he said it was
fine).

Transmissions were rebuilt. props, rudders and shafts were replaced (due a
grounding)

Replaced point style distributors with electronic style (little to no help).

Add "Sea Foam" to gas at each fill.

Looking for a fuel delivery problem while under way at full throttle
position I slowly opened throttle valves (this provided more fuel but
not rpm)

Observed carburetor accelerator pump operation (both jets delvers a full
squirt for each pump)

Adjusted ignition timing to spec. (at idle)

 

[steelespike]

Re: What props should a 1979 Trojan Cruiser have?

A normal motor wide open throttle in neutral would easily exceed self distruction rpm.Wide open throttle application could only be for a second or two or the motor would over rev with possible damage.Lightly loaded boat should reach the motors max reccomended rpm probably in the 4,500 range.
Stumbling and backfiring are classic lean condition or weak or poorly timed ignition.If I understand right you are running different distributors and rebuilt carbs.I would start with them.Perhaps the carb jetting is wrong.Perhaps carb floats were set wrong.Be sure plugs are proper heat range and gapped right.
You could VERY CAREFULLY squirt gas into the carbs while running at speed.
or possibly tickle the chokes if it helps then you have a fuel dilivery problem.
You may be able to check for a stiff transmission by VERY CAREFULLY cranking in forward gear.Then compare in neutral.

 

[DAC68]

Re: What props should a 1979 Trojan Cruiser have?

While looking for a prop answer I stumbled on your inquiry.
It sounds like a timing/fuel delivery problem. Not knowing what you had before your grounding, I cannot say the replacement was incorrect.
No load revs at the dock (I agree with the others, that's not a great idea) will not give the same indications as under load.
You replaced the points/condensor ignition with electronic? Are you getting the correct timing advance at WOT under load? What type of fuel economy are you getting? Is it better or worse given the performance drop you experienced. Are your fuel filters good? Do you have a restriction in the fuel lines from the tanks? WOT under load will use much more fuel than achieving high idle@ no load.
Hope this helps.
Good Luck!

 

[Tail_Gunner]

Re: What props should a 1979 Trojan Cruiser have?

318 chry is a fairly stout motor with a 4 barrel is this what you have?

http://74.125.95.132/search?q=cache...arburetor:+AFB+9263S&cd=1&hl=en&ct=clnk&gl=us

http://store.vintagepaperads.com/servlet/-strse-13400/1977-Chrysler-300-Stern/Detail



Id check your timing first i doubt your running so lean you engines cant rev and if so there running that lean why havnt they popped..


A 318 with a 4 barrel should just light right up to 5000 spinning freely without a hitch.

 

[hwsiii]

Re: What props should a 1979 Trojan Cruiser have?

Erik, if you don't use the boat for bill fishing and don't need to have the big wake for that, I would recommend you need stern lifting props for the best performance overall. The more wake you have behind the boat the greater the drag and the less speed you can get.

Here is the problem...
When I bought the boat we tested the boat at over 31 mph with 5 people on board, rpm
around 3500. With a heavy load 20 mph was normal.

Currently under a no load the best I can do is 28 mph, with a normal load (4-5
people w/o gear) 20 mph and with a heavy (scuba) load 11-14 mph. The engines will
normally provide 2200 to 2500 rpm and seem to be very load sensitive, a moderate
wave will drop speed by 2-5 mph. If one engine stalls (which happens a lot) the
other engine drop rpm significantly. Rapid throttle advances will cause the engine
to stumble or backfire.

It appears you have MOTOR problems right now so don't do anything about changing the props until you get the motors running perfect. You have no baseline until the motors are right. When you get those fixed right come back with RPM data from 2500 to 4,000 RPM and the speeds from GPS and we will get you propped right.


H