Changing Prop Diameter - Briggs outboard

[homemade]

Hello,

It's been a while since I posted, but I've searched as many posts as I can take.

I have a briggs outboard; had it for years; love it; EXCEPT...

On my jon boat, trolling speed was 3mph or so.

I now own a 16 foot neptune sailboat and trolling is 1.5mph to 2mph. Also, I never use more than 1/4 throttle to get to hull speed, but when I go WOT it's is "geared" way too high.

Oh yeah, for those that say trolling at idle is out of the question with the briggs, I've done it for years at the absolute minimum idle speed that it will run. No troubles and no obvious overheating. AND... I can troll all day on 1/2 - 3/4 gallon of gas.

I've looked for a aftermarket prop with lower pitch, but cannot find anything.

ANYWAY...My question is this... Should I shave off 1/2" or so from the outside of the propellar blades?

I am looking to make it less efficient and decrease trolling speed, BUT at the same time, I would like to be able to open up the throttle a time or two (get out of the way of the drunken boaters on our home lake).

I would think that the overall result should be less water moving faster out the back keeping overall force about the same but speeding up the motor in the process.

Does anyone know of any other props that would fit on a briggs?

Any thoughts? Keep in mind, CHEAP FIX!

Thanks ahead of time for your answers.

 

[steelespike]

Re: Changing Prop Diameter - Briggs outboard

For slower trolling I would rig up a trolling plate that can be lowered for trolling, raised for normal operation.If you reach hull speed at 1/4 throttle why bother with full throttle?
Are you worried it can't make its designed rpm?I don't think it will bother
for the short runs you need.If you do decide to try it I think I would start with 1/4 inch.You'll have to be careful to keep it balanced or you will have even more vibration.If it is out of balance it may ruin the bearings and seals.

 

[homemade]

Re: Changing Prop Diameter - Briggs outboard

Thanks for the perspective.

I found a sea anchor, about 14" diameter. I was thinking of using it, but didn't want to get the fish line tangled when the "big one" comes.

I looked into trolling plates, but thought that it would be TOO much drag and would cost fuel efficiency. I like to keep my costs equal to the cost of the fish I catch, so far a day on the water is $15, mostly towing to the lake.

My thought was, that since I have extra RPM's that I don't use, I could "gear it down" so I wouldn't have to mess with changing from "trolling mode" to "cruising mode".

Also, I almost got run over last year and really felt quite helpless. It'd be nice to be able to give a quick spurt of speed without pulling the sea anchor. It's a Neptune 16 foot sailboat; I shuold be able to go 8mph or so, I would think.

Good point about balance. Hadn't really thought of that. Can a prop be balanced on a string or cone setup?

Happy boating.

EDIT --> P.S. Worst that could happen is a $35 mistake for a new prop.

 

[steelespike]

Re: Changing Prop Diameter - Briggs outboard

Rule of thumb your 5hp at wot (wide open throttle)will use about 10% of the rated hp in gph(gallons per hour) 1/2 gph.The same goes for other throttle settings.The idea is to move as fast as possible at each setting.As far as trolling with a plate if you use lets say 3ozs an hour at idle you'll use 3ozs whether your tied to the dock, moving or on a trolling plate.
I would think an appropriate sized plate would give you your required speed,
if it needs to be slower than 1.5.When you start to cut down the prop you may introduce increased prop slip.Might require more throttle for the same speed.Do you feel it can't make the 8 mph as it is?
As you say worse that happens is a new prop.There is a chance a prop shop can take some pitch out of it.They might be able to tell if another prop would work.Some of the old generic motors may use a similar prop.
as far as balancing Not sure of the best way.Any way you try is better than no way.
Good luck Let us know how you make out.

 

[homemade]

Re: Changing Prop Diameter - Briggs outboard

Okay, thanks for your help.

I'll mull it over, but might try to cut the prop anyway (despite all your wonderful alternatives).

Maybe... instead of a motor plate I could use a 2x4 or something and make mounts so it slide up and down on the transom to induce drag. That way it would be easy to pull up if needed and wouldn't get tangled in the fishing line. Hmmmm...

I can go 5mph now with motor bogging hard-core, so I would think 8mph would be feasible. I hear you can plane this boat with enough wind, but probably not with a small outboard. Regardless, not my goal.

Thanks again for helping me work through this.

 

[eddy2419]

Re: Changing Prop Diameter - Briggs outboard

Don't mess with the prop.

Get a 5 gal bucket, plenty on the side of the road. If the handle if screwed up make one out of rope. Cut a 4" hole in the bottom, enlarge if it is too much drag. Tie a 10' rope to the back of your boat. Tie the other end to the handle of the bucket. Drill a hole in the bottom of the bucket near the side. Drill another hole just above that one in the side. Tie a 15' rope through the holes. Tie the other end to the boat.

When you need to go faster or have a fish on, pull the bucket in with the 15' rope or just pull it in enough to "dump" the bucket and cleat it off.

If you don't want to do this this, wrap your prop with a plastic bag and duct tape it on, or just use a few wraps of tape around and through the the prop blades.

Don't cut the prop.

 

[hwsiii]

Re: Changing Prop Diameter - Briggs outboard

Eddy and Steele are right, you will making a big mistake cutting the prop. The chances of you being able to keep it balanced so it won't wear everything out are slim to None in my opinion.

H

 

[homemade]

Re: Changing Prop Diameter - Briggs outboard

Okay... Point taken about bearing wear and an unbalanced prop.

I guess I'll try the sea anchor and see if I can get a fish in without tangling.

I like the duct tape in the prop idea. I might experiment with that.

Thanks,

 

[steelespike]

Re: Changing Prop Diameter - Briggs outboard

I wasn't going to mention this but::
You might be able to drill a hole in each blade.placed very carefully
start with 1/4 inch then either inlarge it or add another as required.
It would help maintain balance.Again as you said the worse that happens is you get a new prop.I like the 2 X 4 idea should be easy to adjust for best speed quickly remove for a swift getaway.

 

[homemade]

Re: Changing Prop Diameter - Briggs outboard

Here's a thought...

I was looking at the 2.5hp Suzuki outboard. Much quieter than the briggs. Do you think this would be able to move a 700lb boat around at hull speed? That should slow down to trolling speed okay.

I can get one new for $699.

Or... Have you guys seen this? http://www.mokai.com/video-preview.html

 

[steelespike]

Re: Changing Prop Diameter - Briggs outboard

It shouldn't take much to reach hull speed.The 2.5 might be enough.
Is the sail boat a full displacement hull or semi planing?
If you don't mind a 2 stroke the Evinrude/Johnson motors 3hp to 8 hp
are excellent motors.All twins routine parts available back to the early 50s
I believe those built 64 on are 50:1 mix.You could a damn nice restored one for $699 or 2 really nice ones.If you run synthetic 2 stroke oil it smokes less and is biodegradeable. bump