Thoughts on speed

[Moody Blue]

Second season with boat and motor. 14ft whaler style boat with 40hp mariner magnum. Worked on the motor, changed prop, and added trim tabs to the boat over the winter. Top speed now with two in the boat is 44 mph @ 5500rpm on medium chop water with peaks to 46mph. Last season the best I could do was 33mph. Will wait for calmer day to try extended WOT operation and handling. This seems real fast for this sized boat. Seemed solid enough and stable at speed but was wondering what others thought. Able to corner at speed with the motor trimmed right down. Am I pushing my luck with this setup ? Any other speed demons out there ??

 

[cobra 3.0]

Re: Thoughts on speed

You gained 13 mph by working on the motor, trim tabs and prop? That sounds incredible!<br /><br />What exactly did you do to the motor?

 

[cuzner]

Re: Thoughts on speed

Hey Rod...thats scary fast in a small boat, specialy with a 40 hp engine. Good job getting to go that fast, what you using for a prop? I,d be careful though, a decent sized wake will get you airbourne.<br /><br /><br /> Jim

 

[Boatist]

Re: Thoughts on speed

When it is rough slow down your boat and Crew will thank you. Also there could be another boat over the next swell you have not seen yet. To see him in big swells you both must be near the top of the swell. Either boat in the between swell and you could be very close to anothe boat and not know he is there.

 

[AntsGrady]

Re: Thoughts on speed

That is crazy fast for a 14'!!! Be careful because if you hit a decent wave you will launch!!! Bet on it!!!

 

[Moody Blue]

Re: Thoughts on speed

Cobra and Cuzner, the extra speed is due mostly to the fact I can run this setup at WOT now. Without the trim tabs I had a whale tail and could only get about 3/4 throttle and it would start to porpoise so bad I would have to back off. I also changed the pitch of the prop from 13" to 15" to bring the rpms to 5500 @ WOT. I can also trim the motor up quite a bit compared to before. Only had it this fast for a few short runs due to rough water on lake simcoe. <br />Antsgrady, did get some air several times already but nothing too scary. Everything seemed "stable" and under control. I'm carefull running in the waves because this little boat can be tossed about easily. My biggest fear is air getting under the boat and flipping it. Is that possible ? The whole rig with me in it only weighs about 800-900 Ib's.

 

[Moody Blue]

Re: Thoughts on speed

I'm not really interested in the high speeds and infact would like to limit the speed for my 2 sons who will be operating it this summer. Can I do the following ? Change to lower pitched prop (not sure what) then limit the throttle travel to restrict the top end speed yet still maintain the correct RPM's. I think this will be better for trolling as well (slower) and pulling a tube or skier. Am I correct im thinking this will work. I am happy at 30-35 MPH with this boat. Don't want anyone getting hurt. What about changing to a 10" pitch prop which should bring RPM's up to about 6500 then restrict throttle to about 80%. Am I correct in assuming the max RPM would then be about 5300 ? Does this make sense ? Hole shot should be a neck breaker, yes ?

 

[cuzner]

Re: Thoughts on speed

Hey Rod, my personal opinion is you your rig is set up perfect, I would'nt change a thing. You don't have to go balls out everytime you get in the boat. If your worried about trolling speed buy a drift sock. If you go to a smaller prop you will have to watch rpm, rip someones arms off skiing, and spend a little more in gas.<br /><br /> Jim

 

[Moody Blue]

Re: Thoughts on speed

OK I agree that I have this dialed in pretty good right now but will what I was suggesting work ? The top end worries me somewhat and I don't want to evaluate the aerodynamic flight characteristics if I can avoid it

 

[Desert_Bassin]

Re: Thoughts on speed

Originally posted by RodC:<br /> I don't want to evaluate the aerodynamic flight characteristics if I can avoid it

RodC, well if the boat has good aquadynamics, shouldnt it have good aerodynamics also? Besides, if you look at this way, a boat is just a rocket sliced in half <br /><br />Glad to see yurs is getting that good, still working on my handling issues.<br /><br />Good luck!

 

[cuzner]

Re: Thoughts on speed

Will it work? probably....but why spend the money and invest the time when you should be out enjoying your boat. A wise man once told me:<br /><br /> " DON'T #$%^ WITH IT IF IT AIN'T BROKE"<br /><br /><br /> Jim

 

[QC]

Re: Thoughts on speed

Rod if you are worried about your sons flying around too fast (I am guessing without you in the boat) you could do some detective work instead of mechanically limiting it. Tell them they have a top speed limit and that's it. If you want to be sneaky you could put a handheld GPS in there, some have a feature that will record the maximum speed . . . Just a thought. <br /><br />You could even tell them that you have hidden one and not do it.

 

[Mahoney]

Re: Thoughts on speed

Have your sons sit with you on some web sites shopping for some replacement parts, drives, engines parts etc, caused by overreving an engine and see the costs involved. Have them pay for the next maintanance round and help you out with doing it.<br /><br />I am not a kid anymore, but money talks and maybe its wishful thinking, but if they have a sort of financial stake in enjoying the boat as well, maybe they will appreciate your instructions a bit better.

 

[Brent223]

Re: Thoughts on speed

I'm very new to boating, but I wouldn't limit the engine/throttle for my kid.<br /><br />Sometimes you need every bit of throttle to get out of a situation. The power is there, in reserve. Same deal on a car.<br /><br />Kids can be taught to respect the equipment and the rules - it's good for character development.

 

[Moody Blue]

Re: Thoughts on speed

Thanks all for your comments. Seems I am worrying about nothing. I will leave well enough alone and run it as is. Besides it'll get me to the fishing spots faster

 

[olefisherman]

Re: Thoughts on speed

had a 16 ft lowe flat bottom with 40 hp merc got in rough water . made it fly balls to the wall . to this day my oldest son will not get in boat with me . he is past 50 now . im sorry i ever did that.
ole fisherman

 

[smokeonthewater]

Re: Thoughts on speed

I disagree..... you do not need to change pitch but I would definately limit throttle for children..... that could get way too dangerous for a kid FAST. You could mechanically limit the throttletr avel and maybe even use a padlock on it..... If they need every ounce of power on that rig to get out of trouble they are in over their heads already and need the leash reeled in.

 

[JB]

Re: Thoughts on speed

Five year old thread, guys.

We encourage you to use SEARCH to see if your question was answered sometime in the past, but PLEASE don't reply to old threads. If you want to discuss the topic further please start a new thread.

Thanks.

 

[Silvertip]

Re: Thoughts on speed

You didn't mention what year the Mariner is but if it has a 1.83 gear set then I question the speed numbers you are presenting. 5500 rpm with a 15P prop and 44 MPH produces negative slip numbers which are impossible. 5451 rpm with a 13P prop produces 33 mph which is a more realistic number since it produces 10% slip which is a realistic number.