Prop size.

[Shrek]

I have a 1972 Columbia 30 which has an atomic 4 with a Walter V-drive and 2:1 ratio. Under the coil, the engine bears the stamp UJ-5 UF (The U and F are overlapped) as in my attached photo.
My question is regarding my prop. It is a 15 x 9 RH prop and the C-30 owners manual called for a 16 x 9 RH prop.
Does my prop have to work harder than a 16 x 9 prop to move the boat 9 inches forward, and result in more load on the engine trying to push the boat, or do I simply have less push from the prop?

On a separate note I have been suffering the issue of shutdowns after 1 hr. of cruising and read the notes re. adding a ballast resistor before the coil to protect it and the EI from getting fried. I used Neil's spreadsheet formula and bought a 1.2 ohm resistor.
I was going to put the resistor on the plus lead going into the coil but have read elsewhere on the forum that when other circuits are also using this plus terminal to supply 12v to whatever, that the resistor needs to go on the minus lead (black) between the coil and the EI
Doesn't this mean that the resistor is now after the coil and not doing what it intended for?
Surely if I fit the leads from the plus side of the coil to the new resistor, and the other end of the resistor to plus side of the coil, only the coil will be affected by the resistor .
Any advice appreciated.

[Dave Neptune]

Shrek, the best way to choose a prop is to check where you are with a tach and a reasonably well tuned engine. You should achieve red-line at WOT and be able to cruise in the intermediate ranges. This is a basic on any marine power plant.

You need to establish the target RPM for your app then you can go from there either up or down in pitch and diameter.

You can check the load with a vac gage and a set RPM point for actual loads on the engine.

It will take about the same power to move your boat 6kts no matter the prop. IE lets say it takes 15HP to move you at 6kts with either prop you mentioned. However they will achieve the 15HP load at different RPM's and throttle (vacuum) settings. And yes there will be a slight variation in frictional drag on bigger blades using a tiny bit more or less power.

Example, my boat cruises at 5.9 kts with my Indigo prop and at the same speed with my 12x10 2 blade. They are both absorbing the same power from the A-4 at 5. kts however the 2 blade does so at 1550 (6" of vac) RPM's and the Indigo at 2,100 (10" of vac) RPM's. The engine is just having an easier time making the 15HP at higher RPM which eases the crank load and engine stress.

Dave Neptune

[Dave Neptune]

Coil

How many power take offs are on the positive post? And what is the voltage at the post when up and running?

Dave Neptune

[hanleyclifford]

Since any advice is appreciated

Mine is to get all that stuff off of coil+ and run separate circuits. IMO the ignition circuit is too important and sensitive to be shared with voltage robbing accessories.

[ndutton]

My question is regarding my prop. It is a 15 x 9 RH prop and the C-30 owners manual called for a 16 x 9 RH prop.
Does my prop have to work harder than a 16 x 9 prop to move the boat 9 inches forward, and result in more load on the engine trying to push the boat, or do I simply have less push from the prop?

To answer your question, the slightly smaller diameter prop is a little easier on the engine and results in slightly higher RPM for the same speed.

. . . . but have read elsewhere on the forum that when other circuits are also using this plus terminal to supply 12v to whatever, that the resistor needs to go on the minus lead (black) between the coil and the EI
Doesn't this mean that the resistor is now after the coil and not doing what it intended for?

The coil is part of a complete circuit and it doesn't care where the resistor is in the circuit. Putting the resistor in the '-' side reduces the current in the coil only (good, up to a point). Putting it in the '+' side affects all circuits connected there (not so good when all you're trying to do is manage the coil amperage).

edit:
And FYI while I agree that all those wires on the coil are a fright (and more common than anyone wants to admit), the only things that 'rob' voltage are poor connections and wire insufficient (too small) for the load combined with circuit length. That's basic electricity 101. Size the wire properly and there's no concern. If the subject is difficult or confusing just let us know, we can help.

references for those so inclined:
ABYC E-9.14e (1) through (4)
National Electric Code 210.19(A)(1) FPN No. 4
Blue Seas treatment on voltage drop https://www.bluesea.com/resources/53...e_Sizing_Chart

[Shrek]

Here is a better view of my attempt to understand my coil wiring. (see new photo) from the + terminal we have the red wire going to the EI module in the Distributor. From the minus terminal we have the black wire going to the EI module in the Distributor and the grey wire which should be going to the Tach.
Then also attached to the + of the coil we have 3 purple wires which I assume, due to their colour, are Ignition related and my ignition sw., is inside the cabin, the Starter sw. in the cockpit, and the Alternator in the engine compartment. I also have an Ammeter.
I believe the other red wire on the coil + comes from the Alternator. I have not traced all of these wires yet but I do know that one of the purple wires is terminated on the ignition switch, which also has a red wire and a black wire on it. Presumably these are a Batt +ve and a Ground.
My new rigging is being tweaked up today as the installation is finalized and the running rigging is changed out today as well. I will try to find time to trace all of these wires and see where they all go. Then I will report back on my findings.
Forgive my ignorance but surely if I leave all of these wires bunched together on one end of the new resistor and attach the other end of the resistor to the coil +, would not the coil be the only thing affected by the added load of the resistor?
I followed the directions given on this forum and input the test results into Neil's calculator and deduced that I needed a 1.1 ohm resistor, but was only able to find a 1.2 ohm example which I hope will do the job.

Thanks as always for any advice given - now, where should I put that resistor???
Gordon Foster (Shrek)

[ndutton]

Forgive my ignorance but surely if I leave all of these wires bunched together on one end of the new resistor and attach the other end of the resistor to the coil +, would not the coil be the only thing affected by the added load of the resistor?
I followed the directions given on this forum and input the test results into Neil's calculator and deduced that I needed a 1.1 ohm resistor, but was only able to find a 1.2 ohm example which I hope will do the job.

Thanks as always for any advice given - now, where should I put that resistor???

Not so ignorant, you are absolutely correct. A buss bar for your ignition wires would certainly tidy things up. BTW, there is no ground on the ignition switch so trace those wires carefully.

To your knowledge, has this coil EVER been involved in a shut down?

[Shrek]

Thanks for the quick reply. This coil has never shut down and the resistor will be added before I take the boat back home to my own marina, 4-5 hours away. The other coils which I believe shut me down have all been deep sixed, as they can no longer be trusted, even from their cooled down resistance readings.
I hope this resistor addition will be the end of my shut down woes and I would like to rewire the a-4 with Moyers rewire kit very soon, should help th tidy up the mess.
I will report my findings later. Busy finishing off the splendid re-rigging job. Photo's will follow. Got it done by the best guy in the area with 30 yrs. rigging/racing experience.
GF

[ndutton]

After your rigging is done I recommend analyzing the ignition circuit for wire size. You have 5 wires on the coil '+' post and at least one supplies the power to the system via the ignition switch. You'll need to determine what the loads are on the remaining four, total the loads and insert the number and the circuit length into the voltage drop calculator found in the ABYC and USCG Standards forum category.

Since you used our calculator you can figure 3.4 amps for the engine ignition (EI system) and 3 amps is a safe estimate for the alternator excite wire. Beyond that you'll have to trace where the wires go and determine their loads if any. Your goal is no greater than a 3% voltage drop on the entire circuit.

[hanleyclifford]

Here is a better view of my attempt to understand my coil wiring. (see new photo) from the + terminal we have the red wire going to the EI module in the Distributor. From the minus terminal we have the black wire going to the EI module in the Distributor and the grey wire which should be going to the Tach.
Then also attached to the + of the coil we have 3 purple wires which I assume, due to their colour, are Ignition related and my ignition sw., is inside the cabin, the Starter sw. in the cockpit, and the Alternator in the engine compartment. I also have an Ammeter.
I believe the other red wire on the coil + comes from the Alternator. I have not traced all of these wires yet but I do know that one of the purple wires is terminated on the ignition switch, which also has a red wire and a black wire on it. Presumably these are a Batt +ve and a Ground.[ATTACH]11677[/ATTACH]
My new rigging is being tweaked up today as the installation is finalized and the running rigging is changed out today as well. I will try to find time to trace all of these wires and see where they all go. Then I will report back on my findings.
Forgive my ignorance but surely if I leave all of these wires bunched together on one end of the new resistor and attach the other end of the resistor to the coil +, would not the coil be the only thing affected by the added load of the resistor?
I followed the directions given on this forum and input the test results into Neil's calculator and deduced that I needed a 1.1 ohm resistor, but was only able to find a 1.2 ohm example which I hope will do the job.

Thanks as always for any advice given - now, where should I put that resistor???
Gordon Foster (Shrek)

The better picture of the coil "ganglia" introduces the possibility that a too small wire may be feeding multiple users and that is a big no-no in propagation of electrical "trees". To clean things up I suggest the introduction of a buss bar fed from as close to the batteries as possible, probably from batt switch common or a main buss bar if you have one (I use a #8 just to make sure I have capacity for expansion). From that buss bar send a dedicated #14 to the resistor, thence to coil+ with nothing else along for the ride. Then feed the other items from the buss bar.

[Shrek]

Very busy day today and tomorrow doing the running rigging, adding mainsail reefing and lazy jacks. Thanks for all the support and I will report back when I can get a breath in.
GF

[ndutton]

You're not alone

Gordon, here are a few pictures from this forum showing that your coil stack is pretty common. I'm posting these uncredited to protect the innocent.

Something I wanted to point out in your recent picture, something to think about when you get around to rewiring, something to avoid. The circled area shows wires run over a sharp edge, a virtual guaranty of a future chafe-through and circuit failure.

[hanleyclifford]

No Need to Protect The Innocent

The picture in the middle is my boat, Destiny. I did not mean to suggest that no wires other than the feed to coil+ and the black EI wire should be on the coil. There are numerous other wires on both coil terminals that need to be there - but they should not be big load carriers such as pumps/blowers etc. On my coil, the picture in the middle, on coil- we have the black wire from the EI and the sensing wire from the tachometer (almost no load). At coil+ I have the red wire from the EI, the pink wire from the "R" terminal on the solenoid, the supply wire for the tachometer, the power feed from the resistor, and voltage sensing wire (the white one) so I can monitor voltage at coil+. This voltage remains steady because no significant loads are fed from coil+ except the ignition.

[hanleyclifford]

BTW, Neil is right about those wires running over the head and down over a corner - between chafing and dry out from heat they could have a short life. If you can do it, it is best to re locate the coil off the engine to another location, as in the case of two out of three of the "innocent".

[roadnsky]

As others have noted, I too am a big fan of using a buss bar to take the "load" off of the coil terminals.
Then you can have a nice clean coil install without the "Christmas Extension Cord" effect hanging on your coil...