MisterGuru Posted July 5, 2005 Share Posted July 5, 2005 Update - I have a tach now and with a "normal" load I am running 19mph at 4300 RPM I have a 15 foot fiberglass deep semi-V hull with a LOT of plywood which equals a lot of weight. The hull was originally bare, but has about 3 sheets of 3/4" plywood for decks, 3-4 eight foot treated 2x6s, light carpeting, 12 gallon gas tank, 40# trolling motor, outboard/steering console, 40 lbs of tackle, etc... My 1977 40hp Mercury has a 13 degree aluminum prop and with me and my daughter it will run 20 mph on the GPS. Add my wife and my other daughter... 18mph, and last night I added a friend and his camera equipment (fireworks pics) - about another 350-400 lbs, and 13.5 mph was tops. I don't think I have any trouble with my "holeshot" but it makes sense to me to drop down in pitch to get RPMs up.... but the boat does seem to take off well, even very heavily loaded. So maybe I am confused and should go with more pitch... I do not have a tach... sorry for lack of info. Is there an obvious direction to go here? Quote Link to comment Share on other sites More sharing options...
Nick_Barr Posted July 5, 2005 Share Posted July 5, 2005 Well, i would first buy a very high performance prop, the i would fiddle around with the tilt positions to get max speed, Last get a jackplate. Thos are all i can think of. Quote Link to comment Share on other sites More sharing options...
gamblerOH Posted July 5, 2005 Share Posted July 5, 2005 It sounds to me like you are already propped good. If your boat will come out of the hole with that heavy load then I wouldnt mess with it. 13.5 is not a bad speed for a already heavy boat hauling a heavy load.I'm sure you were way over the coast guard weight limits for that boat. Mine is a 20 footer and is only rated for 4 people or 600 lbs. I had a 40 merc a long time ago and it would not run over 20 with just 2 people (we were kids about 135lbs each) so I think you are in good shape already.I dont think you'll be needing a performance prop and a jackplate though Quote Link to comment Share on other sites More sharing options...
MisterGuru Posted July 6, 2005 Author Share Posted July 6, 2005 I dont think you'll be needing a performance prop and a jackplate though Dang! Maybe the shop will return this stuff :-) I went ahead and got a tach for the blue montser. I hate having a vehicle without a tach... It was $70 for the tach... oh well, we will see what RPM I am turning. Thanks. Quote Link to comment Share on other sites More sharing options...
gamblerOH Posted July 6, 2005 Share Posted July 6, 2005 Good idea, the tach will tell you all you need to know. I hope you went ahead and got some hydraulic trim tabs to go along with your jack plate and performance prop, you could also think of adding nitrous ;D. Really though if your rpms check out good I would leave it alone. I just talked to a buddy of mine whose 40 hp on a 17 ft. aluminum does well with light loads but gets really slow with heavy loads,like I said earlier you were most likely hauling more weight than the boat was designed to handle. I hope the shop will take back the stuff you went out and bought, its gonna be tough if you have to loose a couple grand on performance parts ;D Quote Link to comment Share on other sites More sharing options...
MisterGuru Posted July 6, 2005 Author Share Posted July 6, 2005 Thanks for the encouragement, but I had already fabricated a plywood box to mount the roots-type blower, and the butterfly scoop looks very cool on the outboard's hood. I can mount the tach in the center hole of that! The blower is just a 471, so a couple of coats of JB Weld on the seems of the plywood box xhould hold it. I will be getting 26-28 mph very soon! Yee haw! Quote Link to comment Share on other sites More sharing options...
gamblerOH Posted July 6, 2005 Share Posted July 6, 2005 Never thought of adding a blower, Im ordering one today ;D Quote Link to comment Share on other sites More sharing options...
MisterGuru Posted July 11, 2005 Author Share Posted July 11, 2005 I have a tach now! OK, well I am traveling 19 mph today at 4300 rpm when at WOT. The info I gather says my 40 HP should run about 5200 rpm... so 900 rpm too little... I should go to a 9" prop ( I am at 13 now) right? Any input? Quote Link to comment Share on other sites More sharing options...
gamblerOH Posted July 11, 2005 Share Posted July 11, 2005 It sounds like you may have other problems, such as a dirty carb etc. I think a 13 is good for your situation, I wouldnt think you would need to drop more than one or two sizes at most. I would be sure that your engine is running right before doing anything. Quote Link to comment Share on other sites More sharing options...
skeetermike Posted July 11, 2005 Share Posted July 11, 2005 5200 RPM'S GOOD GOD! My 18.7 skeeter with a 150 merc. and a 23 pitch prop. won't turn out but like 5700 or so. I used to have a 14' alumaweld jon boat with all that heavy 3/4 plywood for decking, a built in live well, and me and my buddies fat a** and we could still hit 20mph!! I had a 20 mariner motor on the back. You might check and see if your boat is maxed out with that 40 horse on it. I know my skeeter is lil slower but it is rated for a 175 also. I did used to sink rocks for cover and when I would load it down and head to my spot to sink those rocks the extra wt. really slowed me down too. I even tried pulling my gf's lil sister behind it on a tube and it pulled the engine way down. Those small motors just ain't made to pull heavy loads like that. Quote Link to comment Share on other sites More sharing options...
MisterGuru Posted July 11, 2005 Author Share Posted July 11, 2005 I ordered a 10" Michigan Wheel Vortex 4 blade. I will post the results when it comes in. The info has to help someone! Quote Link to comment Share on other sites More sharing options...
Pa Angler Posted July 12, 2005 Share Posted July 12, 2005 Question? Isn't a four blade prop more for torque than top end just something I thought read somewhere. Yes after checking my Bass and Walleye boats August 2005 magazine, Yes August it does say that a four blade will help get a heavy load to plane quicker and turn better but are a tad slower on the top end. You should pick this magazine up it has a very good article on props and a listing of props by manufacture. You also might want to call mercury or email them about your situation. Although sounds to me with the extra weight you need a bigger motor a prop can only tune performance so much 40hp will still be 40hp no matter what prop you put on unless your motor is out of tune and your onlly geting 30-35hp out of it. A stainless steel prop will give you more top end though because it won't flex under load like an aluminum prop does. I have a friend that is running a 16' mirrorcraft aluminum Deep V refitted with plywood such you have done with a 35hp Evinrude with an aluminum prop and gets about 17mph on a lake with no current with two adult males and gear onboard. You said yours is 15' fiberglass which most times will weigh more than it's aluminum counterpart. So maybe where your at is as good as it gets but don't give up get trying and good luck. Chow The Pa Angler Quote Link to comment Share on other sites More sharing options...
scbassin Posted July 14, 2005 Share Posted July 14, 2005 If it's hot & humid where you are you will lose 300 to 400 rpm anyway. I would get a 3 bladed stainless steel prop before doing much else. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.