3200 RPM Max, 225hp LM318....

[Paul - SW Ontario]

Well here we go...I have painstakingly searched and read every thread on every forum including our Trojan, and MarineEngine etc.
Any and all threads pertaining to the inability to reach WOT under load.
Every possible reason and solution has been addressed by our Forums' Elite, yet there are still a number of fellow boaters still trying to solve this problem....some like myself, for several seasons.
From carbs to anti-siphoning valves, fuel filters to enthanol, engine timing to worn out dizzys, electronic ignition to air flow...as well as HP/weight ratio, clean bottoms, and props. The list goes on.
A few threads have resulted in the OP solving their issue, but many of them have died out resulting with OP issue unresolved and frustrated.

I'm wondering if one of our own or known someone who has had this problem and found a solution over the course of their time spent on the water?

For the record....re-finished two part polyurethane bottom with single coat ablative bottom coat, new (factory spec) 14x10 RH Nibral prop with cup & cutlass bearing, new Edelbrock Marine carb to spec (old Carter had the same RPM issue), no anti-siphon valve (factory arrangement), new clean fuel pick up tube, water separating fuel filter and factory steel filter at carb, stock fuel pump that shoots a healthy 5' stream of fuel, new points, condenser, cap, coil, wires, plugs, healthy compression, and spot on engine timing (with what appears to be a nice curve though the advance)....fully functioning trim tabs. Dual exhaust with nice flow of water
The engine was proffessionly rebuilt in 2004....has 430 hours and runs beautifully with full WOT in neutral (done only quickly a couple of times through the years to be sure it can)
The first few years I owned the boat it had the original tach that was not functional, so I had no indication of rpm...at which point I installed a new tach that has been proofed by measuring the rotational speed of the 1:1 ratio spinning prop shaft coupler with a tach gun.
I comfortably cruise at 2900 RPM and 16.5 -17.5 knots.
The only thing I haven't replaced is what I assume is the original but very good condition (shaft play & advance weights/springs) Prestolite Distributor.....even tried the electronic ignition with no improvement.
I have 35 years of mechanical background in racing/designing and building stock cars and modifieds, including their engines....but this has me stumped I must admit.

[AwayOnBusine$$]

Pretty much in the same boat twin 318s

[Paul]

Hi Paul,

I know that you've done allot of work to your boat over the years which makes me wonder how much extra weight you've added with upgrades. When I first got my 26 I installed the 350 and was turning a 14 x 10 prop which allowed me to hit 4700 rpm. As years went on with the addition of a generator, AC and lots of other weight I fell out of my desired RPM range. On a recommendation from Michigan Wheel I installed a DynaJet 13 x 10 Nibral Cupped prop. This brought me up in RPM however it did not have enough blade area to handle the HP from the 350 very well. It probably would have worked well with the original 228 HP 305. The next prop I tried was a 14 x 9 DynaJet which was the same prop that was on the boat when it had a 305. This prop put me back in the middle of the desired RPM range.

Its amazing how much the addition of extra weight can affect the performance, especially in a single screw. I still have the 13 x 10 NiBrAl Cupped Dynajet in its original box. I'd be happy to lend it to you if you want to try it out, it would probably run well on a 318.

Let me know.

[prowlersfish]

Paul # 2 is right on IMO , Just because a boat can with XxX size prop doesn't mean its the right prop now . The prop the boat to get the max when new . The new boat is dry dry dry . The new boat doesn't have all the gear we added . the hull , stringers decks even the glass have some more moisture in them it all adds up . I would down size a little on the prop my self .

Paul #3

[Paul - SW Ontario]

This is true, I have calculated about 810 lbs additional weight, which is more or less 15% more then the factory 5400 lbs.

That being determined a few seasons ago, I took the liberty of emptying the entire boat of anything and everything that wasn't bolted down...even bow and stern anchors (was amazed at what I removed, lol)
Me and my wife, 1/4 tank of fuel, empty fresh and black water tanks...away we went.
Exited the marina, got up on plane....resulting in 26.4 mph at 3400 RPM

Now I knew that conflicted with the factory speed overground specs for 3400 so I compared the tach reading with my laser gun on the prop shaft during this trial, and confirmed the reading was correct. Very odd...

I have no doubt about HP vs. weight ratio when it comes to a boat's overall speed and performance..(my years of racing is based on that equation)...and I am willing to concede that this is in fact my problem with wide open throttle while weighted down, especially with little or no prop slip. The boat' speed over ground is purely a result of a given prop and it's specs (especially a 1:1 drive ratio) as it cuts through water at a given RPM (as Paul referred to with his Dyna Jet)...

But, why when my boat is stripped down weight wise, is it I cannot get past 3400 RPM ? Regardless of speed...

[Paul]

... why when my boat is stripped down weight wise, is it I cannot get past 3400 RPM ? Regardless of speed...

In propellers, the blade area should be directly proportional to the horse power being applied to it. That being said, too much area can load up the engine a little too much before it hits its optimum RPM. Reducing the diameter to reduce the blade area or dropping a pitch to say a 14 x 9 is sure to free up another few hundred RPM for you and may just allow your engine to get deeper into it's power band. When you start looking into it, propping a boat correctly can be a real science in itself.

Actually, I'm surprised that you're getting 26.4 mph at 3400rpm. I know that my boat is pretty heavy but I have to turn 4000 rpm to hit that speed. If you want to experiment a little bit, I have the 13 x 10 NiBrAl Cupped Dynajet prop that I mentioned earlier as well as a 14 x 9 NiBrAl Cupped DynaJet that I can lend you to try out if you'd like. Let me know and we'll make arrangements.

The one that I have on my boat currently is a 14 x 9 NiBrAl Cupped DJX which has more blade area than the 14 x 9 DynaJet. . I lost 100rpm when I replaced the DynaJet with this prop however I picked up 2-3 mph.

[Paul - SW Ontario]

... why when my boat is stripped down weight wise, is it I cannot get past 3400 RPM ? Regardless of speed...

In propellers, the blade area should be directly proportional to the horse power being applied to it. That being said, too much area can load up the engine a little too much before it hits its optimum RPM. Reducing the diameter to reduce the blade area or dropping a pitch to say a 14 x 9 is sure to free up another few hundred RPM for you and may just allow your engine to get deeper into it's power band. When you start looking into it, propping a boat correctly can be a real science in itself.

Actually, I'm surprised that you're getting 26.4 mph at 3400rpm. I know that my boat is pretty heavy but I have to turn 4000 rpm to hit that speed. If you want to experiment a little bit, I have the 13 x 10 NiBrAl Cupped Dynajet prop that I mentioned earlier as well as a 14 x 9 NiBrAl Cupped DynaJet that I can lend you to try out if you'd like. Let me know and we'll make arrangements.

The one that I have on my boat currently is a 14 x 9 NiBrAl Cupped DJX which has more blade area than the 14 x 9 DynaJet. . I lost 100rpm when I replaced the DynaJet with this prop however I picked up 2-3 mph.

Paul, I would definitely be interested in trying one or both of your props when we splash in the spring....and if one of them improved my performance, I would certainly be open to buying it from you if you were willing to sell.

I have a spare cupped NiBrAl 14 x 10 that I was going to send out to be refurbished...I think I will hold off for now.

I agree that I'm on the low side the power band curve at 3200 RPM. Although that's a comfy cruise point, I lack the maximum ability to grind it out in the chop and confused waves we commonly deal with in the Long Point Basin.

My F25 weight usually runs in the 6200-6500 lb range depending if we take the dinghy and outboard...I get these numbers from weighing it a few times (minus the trailer weight) at out local TA scales.

I believe you are correct Paul in your assumption with the props, although a few hundred RPM improvement puts me higher in the cam torque curve, it would be interesting to see if I can actually get WOT with either of those choices.

It is truly a science.

[mikeandanne]

Heh Paul.....one question for you, have you put timing tape on and plotted the advance curve, whats your total and is it in by 2800 or there abouts and got to hit the appropriate rpm , advance degree spots.....I have much the same racing background as you just drag cars, anyway if your curve aint right the engine will never go ahead under load which I am sure you already know......now that said, from the other Pauls numbers it looks like you might be over propped a bit. So just a bit of rambling from me.
One more thing, still not convinced that ablative paint doesn't have a bit of drag to it, maybe the new stuff is better I don't know.....

[Paul]

Sent you a PM

[Paul - SW Ontario]

Heh Paul.....one question for you, have you put timing tape on and plotted the advance curve, whats your total and is it in by 2800 or there abouts and got to hit the appropriate rpm , advance degree spots.....I have much the same racing background as you just drag cars, anyway if your curve aint right the engine will never go ahead under load which I am sure you already know......now that said, from the other Pauls numbers it looks like you might be over propped a bit. So just a bit of rambling from me.
One more thing, still not convinced that ablative paint doesn't have a bit of drag to it, maybe the new stuff is better I don't know.....

Hi Mike,

I agree that ablative bottom coat will have some drag....measurable?...Maybe. But I had basically the same results for the 2014 season where I had only the fresh 2 pt. poly painted bottom. I added the ablative in 2015 cuz of our slimy standing water in our marina slip.

I also agree that with the permanently added extra weight on my boat, that it has likely resulted in the factory prop not being ideal now...1000 RPM difference?...I believe it could be.

As most of us on the forum know, the un-availability of the whole marine Chrysler small block timing curve specs/ graphs etc. has been a mystery.

My base timing for a four barrel SB is the factory 6 degrees B.T.C. @ 750 RPM...then adjusted back to 650 RPM for normal operation. Full advance is 26 degrees at 2500 RPM. The advance curve with the timing light shows a fairly smooth consistent advance thru 650 to 2300 (yes, not a 'curve' but)

Obviously the springs on the mechanical advance weights control this curve and are not adjustable (at least not to any accurate degree in boat)...and the seemingly impossibility of finding new springs here in Canada, and the lack of curve specs to be found...I've succumb to the idea that what I see when watching the dizzy advance is as good as I can get.

I've considered a new distributor with electronic ignition, but there goes another $1K Canadian.

I'm accepting Paul's offer of trying his props and seeing the results...then decide if a new distributor is in order.

These two approaches to the issue seem to me all that's left to try.

Like I mentioned in the original post...was just wondering if anyone has had this problem and found a remedy they would like to share, maybe I'm still overlooking something.

I know I'm not the only one, lol....

[mikeandanne]

FYI....curves from mallory marine distributor..cant take credit for the nice graphs but when I checked these against the mallory distributors on the boat it was almost dead on , maybe one degree off in spots which is nothing........Mike

[Paul - SW Ontario]

... why when my boat is stripped down weight wise, is it I cannot get past 3400 RPM ? Regardless of speed...

In propellers, the blade area should be directly proportional to the horse power being applied to it. That being said, too much area can load up the engine a little too much before it hits its optimum RPM. Reducing the diameter to reduce the blade area or dropping a pitch to say a 14 x 9 is sure to free up another few hundred RPM for you and may just allow your engine to get deeper into it's power band. When you start looking into it, propping a boat correctly can be a real science in itself.

Actually, I'm surprised that you're getting 26.4 mph at 3400rpm. I know that my boat is pretty heavy but I have to turn 4000 rpm to hit that speed. If you want to experiment a little bit, I have the 13 x 10 NiBrAl Cupped Dynajet prop that I mentioned earlier as well as a 14 x 9 NiBrAl Cupped DynaJet that I can lend you to try out if you'd like. Let me know and we'll make arrangements.

The one that I have on my boat currently is a 14 x 9 NiBrAl Cupped DJX which has more blade area than the 14 x 9 DynaJet. . I lost 100rpm when I replaced the DynaJet with this prop however I picked up 2-3 mph.

Hey Paul....the weather has obviously been less then desirable so far this spring.
Weather permitting, we are planning to haul the Trojan down to splash it this coming Sunday.
I have installed your your 13 x 10 prop to try first...

The goal is to have the boat at it's typical weight at which we normally cruise with. Therefore we will have our dinghy & outboard on our swim platform. We are also starting out with a full fuel tank (which would be about the same as a half tank of fuel, half tank fresh water, and some in the waste tank)

Taking the prop puller and your 14 x 9 to try as well, if need be.

A huge Thank You is in order for your help.

Will let you know the results, if all goes as planned this weekend.

Cheers!

[larryeddington]

Wonder could we save those charts here on our web site. I notice one is a jpg and the a png. Would be nice to have a copy of the originals available on website tech.

[Paul]

Good to hear Paul, I'll be interested to hear the results. My guess is the 14 x 9 will end up giving you better results however only testing will tell. I'm not in a big hurry to get the props back so if you would like to try them both under varying conditions, take your time and do that.

[larryeddington]

I have an F28 with twin 318s and it has, I believe the orginal 14x11. As I had a parts f28 I had two extra props and had them cut back to 14x9. I had the same problem and hope this fixes it. I have not tried the 9s yet but looking forward to your or my results.