15' trihull with 70hp johnson

[steveo32]

Hi, this is my first boat and I was wondering what I would be able to do with it besides fishing. I have a tube that came with it that is still new in box, it is 4ft round and I bought a tow rope 60ft. Just wondering if I would be able to ski with it? I don't plan on doing any competitions or anything just want to have a little fun. I know it can handle a tube and kneeboard, because my friend has a 14ft aluminum starcraft with a 50hp johnson that I have tubed and kneeboarded behind. I have never skied before but until last year I had never kneeboarded either, I found that the trick is getting up once you do it it is easy. I will not be slalom skiing, just regular two ski or maybe the new wider 2 skis. Just wondering what your recommendations are and can you buy ski handles that attach to your ski rope or are they all on piece? Thanks

 

[tashasdaddy]

Re: 15' trihull with 70hp johnson

sure you can ski with it, i learned as a kid, behind an wooden fishing boat, and a 1955 15 hp evinrude. we use to make handles out of a broom stick and some rope. http://www.overtons.com/modperl/product/catalog.cgi?r=browse&aID=1G&cname=Ropes-Handles

 

[ebry710]

Re: 15' trihull with 70hp johnson

I used to ski behind a 15' boat with an Atwater 50 hp engine. Of course with that configuration you had to get up with 2 ski's then drop one once up.

I also currently have a 15' Marlin (trihull) and other Marlin owners have said it ski's great with a 70 hp outboard. Mine as of yet does not have a engine.

 

[Frank Acampora]

Re: 15' trihull with 70hp johnson

That will be a very nice combination for skiing, wakeboarding, and tubing. The 70 Rude is a beautiful, well designed engine. It is big enough to pop you out of the water fairly quickly yet small enough that it won't kill you on gas mileage. But, even with that, don't be surprised at what a day on the water will cost. Water sports really suck up the gas.

A tube rope should be dedicated to tubing; you need to by a ski rope (they come with handles) for wakeboarding and skiing.

As you get more proficient at skiing with two skis, learn to slalom--once you do, you will never go back. It actually is easier and more maneuverable than two skis--It's just a little more difficult to get up on it.

 

[bigjayhoffman]

Re: 15' trihull with 70hp johnson

I agree with what everyone is saying here. I have a very simular boat
15 foot Rinker trihull with a 70 on the back.
Works great for tubing and skiing. It can pull me and I'm 250 lbs. It takes a bit but once it gets outta the hole, im laughing. and then tubing my boat gets to about 22 to 28 miles an hour while towing someone.
I do notice quite a bit of drag when someone drops to one ski though...


but besides that just put that tuber into a whip and watch them hang on for dear life

 

[DJ]

Re: 15' trihull with 70hp johnson

Here's a tip.

The 70 (triple looper) OMC is a real puller if:

1. It's in good tune.

2. It's prop'd right.

That engine needs to be able to turn 6000 RPM, with a very light load, to be able to pull skiers, all day and live.

That means a relatively low pitch prop.---13" X 15" would usually do it, on that boat.

 

[steveo32]

Re: 15' trihull with 70hp johnson

The OEM replacement is a 17" prop, and I just ordered one. Will I still be able to ski behind it, I do not have a tach so that is why I went with the OEM replacement size. I have cleaned the carbs and replaced the spark plugs and checked all the wiring for wear and tear and everything looks good. And it runs well with the muffs on. It obviously revs higher with the muffs because there is no water to create a resistance. I wouldn't think that there would be too much change from 17" to 15", that should only change the wot rpm by 200.

 

[BF]

Re: 15' trihull with 70hp johnson

Hi...

A couple points....

2" of pitch makes much more difference than only 200 rpm at WOT. It can be the difference between a boat that really labors to get on plane to one that accelerates well. If it's a bit overpropped it can mean that with a skier in the water, the motor doesn't make enough power to get on plane. So, until you try it, you won't really know. Also you can watch out for other with the same motor as you, and a similiar boat and ask them what their setup is. If you put 4 adults in the boat and see how fast it is to get on plane, that will give you an idea of how it will be with a lighter load + a skier.

You might consider adding a tach to your console.

From your last post, it sounds like you are rev'ing up the motor on the muffs... that is a no-no. Don't rev it much above idle. Carbon in the engine and the lack of backpressure on the exhaust can cause "run away", if rev'd up on the muffs. It's where carbon gets hot and acts like a spark plug and the engine rev's up as fast as it can. Turning the key off won't stop it either. Even if you disconnect the fuel line, the fuel in the carbs can keep it running long enough to do serious damage. Do a search on "run away" and do some reading here.

As has been said, yes, best to buy a dedicated rope for skiing. Some (better ones) do have a removeable handle, but the tubing ropes tend to be heavier than ski ropes. Ski ropes will allow a bit more stretch.

If you don't have a ski pylon, get a harness with a pulley/float that connects to the 2 eyelets on the back of the boat. Connect your rope to that.

good luck.

 

[steveo32]

Re: 15' trihull with 70hp johnson

Thanks for the advice, I only rev'ed it up once but not full throttle by any means only about a quarter and I could tell that it was whinning out pretty good, so I put it back down to idle. Also I do already have a harness pulley for tubing. I will see how it does with 4 people when it finally warms up here, can't beleive it is spring and we are still in the 30's. Hopefully the lakes melt soon.

 

[steveo32]

Re: 15' trihull with 70hp johnson

Also, what would you reccomend for ski rope lengths??

Also I know a couple people said they had a similar setup to me in this thread, what are you running for a prop, diameter and pitch and what is your engine and hull length. My prop 13 1/4" X 17" this is the OEM for a 75' 70hp triple loop Johnson.

Thanks

 

[bigjayhoffman]

Re: 15' trihull with 70hp johnson

Hey i just checked out the prop on my 79 Merc 70 horse the boat is a 74 Rinker at 15 feet 6" and the numbers on the prop are 10 3/4 R13WC

Is that right ??
I know nothing of props
only guitars

 

[steveo32]

Re: 15' trihull with 70hp johnson

i'm not sure, it sounds like your diameter is 2 1/2" smaller than mine and your pitch is 4" smaller. I know that diameter and pitch both play a role in top speed and whole shot speed. I have a thru hub exhaust, and probably a larger gearing, that maybe why your diameter is so much smaller. Like I said this is just a guess, I am new to boating also. Does anyone have an OMC Johnson/Evinrude outboard of similar horsepower? And what do you run for pitch and Diameter?

Thanks

 

[BF]

Re: 15' trihull with 70hp johnson

I can't give you any more prop advice, 'cause my rig's not like yours. But as for the ski rope... 75 or 60' are the common lengths. I prefer 60' for general use. If you are pulling kids or otherwise driving fairly slow, at 75' they're way back there, almost with 2 sets of waves for the wake.

For kneeboarding or wakeboarding, you want to adjust the line length shorter so that the wake is nice at the speed used. This is a good reason to buy a better rope, like a slalom rope. It has removable lengths and can easily be adjusted to be shorter than the full 75'. The first section will be 15' off and get you to 60'.

good luck

 

[steveo32]

Re: 15' trihull with 70hp johnson

Thanks for all the advice, I really appreciate it.

 

[hibbert6]

Re: 15' trihull with 70hp johnson

Hi. I have a 15' tri-hull with a 65hp Merc. We pull a 150lb slalom skier with it. Two years ago I replaced my prop with a Piranha 13x15 composite prop.(Stock 3 blade pitch). I like it a lot. However, the next day I saw an ADJUSTABLE composite 4 blade prop at the boat store for about the same price I paid for mine. It allows you to adjust the pitch up or down a degree, (14-15-16 on a 15 pitch prop). Sure wish I'd gotten that one!

Dave