how fast?

[joonch65]

Yesterday I bought a 16' ski barge w/75hp Johnson w/jet unit.what kind of speed can I expect? When I test drove with 3 people in the boat it only did maybe 25mph.the boatis really light it seems it should go a little faster. in relation to the bottom of the boat where should the water intake be? and what angle should it be? could any of this have any effect on speed? The motor(its a 1976) has 30 hrs on a rebuild. I checked the compression its 150 all three cyls. could the pump not be performing up to snuff? Thanks for any info. J

 

[DJ]

Re: how fast?

joonch65,<br /><br />Outboard jets are not very efficient.<br /><br />The 75 hp is at the powerhead. Factor in the jet pump and you're probably closer to 50 hp, actually realized.

 

[JasonJ]

Re: how fast?

I think it was going about as fast as it could go. One way to make it go faster is to leave the friends at the dock, that'll give you more speed. You could look at your setup, make sure it is trimming properly, and make sure you are not carrying needless weight. Otherwise, thats about it. Look on the bright side, at least you are out on the water enjoying the day. May not be fast, but it beats sitting on shore

 

[ZmOz]

Re: how fast?

I don't know if there's any reason you specifically bought a jet, but the only way to go faster would be to put a regular lower unit on it and a prop. Jets are extremely inefficient. I would guess even less than 50hp at the impeller, considering the fact that old motors are rated at the crankshaft.

 

[detailman]

Re: how fast?

if you want to make it faster apply silon to the hull. typical results on my customers is 5 to 8 more mph.i have it on several boats and the #1f14 pilot in the world has it on his jet.

 

[joonch65]

Re: how fast?

Thanks for the info. I got the jet because I've got a boat ramp on the Feather river about 3 mins away but you need a jet.You dont absolutely have to have jet but there are alot of snags and shallow area so why worry?I know they lose alot os power with the pump but I figured the thing might do 30 with just me in it. I havent tried it out yet by myself (cuz I screwed up the fuel pump and I wont get parts till mon.)but Im curios to sed what happens.What is silon and where do I get it. It sounds like it might be worth a try.

 

[Mercury140-I6]

Re: how fast?

I think he means silicone, but a good quality wax (like "Liquid Luster") does the same thing. ZmOz is correct in that your motor was rated 75hp at the crank shaft. Adding the jet pump takes 30% off the top, that makes it about 52hp with a prop of that time period, or about 40 - 45hp at the prop for a newer motor just to give you a comparison to performance. Have a blast with it and try twaxing the hull. You might be surprised at what you get. I picked up 5-7 on mine.<br /><br />Craig<br /><br />(My baby)<br /> http://www.myfishingpictures.com/showphoto.php?photo=13003&sort=7&thecat=500&password=

 

[Link]

Re: how fast?

Pumps are GREAT but like other's have said your fighting a loosing battle here on top end speed.<br /><br />There are several factors concerning the HP rating of outboard jets vrs props. And the factory for outboard jets has mis-lead in advertising for years!<br /><br />Both are using Torque power at the prop or impeller in a controlled situation/test tank.<br />There the pump only loses about 1/3 of the power!<br />So say a boat rated at 50hp prop would only need a 75HP motor to preform the same. Like pulling a skier out of the water! This is true!<br /><br />But here is the difference between prop vrs pump.<br />As the boat increases in speed the prop is still using high and low pressure like a airplane prop.. except for RPM it doesn't matter.. but the pump pushing water as it (the boat) increases in speed the the water jet pushing the boat decreases.. so you don't get the same speed.<br /><br />From stop to WOT a 75HP pump will do as good as a 50HP prop on the same boat. But after that the pump sux big time.<br /><br />Sorry about the edit but thats what I get for trying to do three things at a time, talk on the phone, type and think <br /><br />My 14ft sled with a 45HP prop did between 40-45 mph and I had to put trim tabs on it just to keep it from flipping. The same boat now with a 90HP pump I'm lucky to get 31 mph. But gets up on step real Quick <br /><br />Link