Mariner 30 - A bit slow or not?

Got a new engine for my 11ft sports dory, it's a Mariner 30 manual start. Not too sure of the year but I have been told it's early 90's.

The boat weighs 79kg and the engine must be around 55kg - 60kg and with 2 persons on it going flat out we managed 26mph (total weight around 300kg).

Is it me or is that a bit slow? + Would hydrofoil fins make any difference?

Can't get any more info on the engine as I don't have a serial number but here are some photos of it.

http://i300.photobucket.com/albums/nn17/djneily/M30a.jpg

http://i300.photobucket.com/albums/nn17/djneily/M30b.jpg

http://i300.photobucket.com/albums/nn17/djneily/M30c.jpg

http://i300.photobucket.com/albums/nn17/djneily/M30d.jpg

http://i300.photobucket.com/albums/nn17/djneily/M30e.jpg

Re: Mariner 30 - A bit slow or not?

Looks like your garden-variety Yamaha-ha-ha!!!

Engine appears very clean, prop's not chewed up, one observation is that this motor is a Longshaft (20" transom).

If your 11' boat has a Shortshaft transom, the motor's gonna stick down an extra 5" and that's a lot of drag. I'd think that the motor should push that boat 30+, but you'd lose a fair amount of speed from xtra drag.

If you measure from the top of the transom where the motor sits, to the bottom of the keel (or what would be the bottom of the boat depending on how the hull is configured) and you get somewhere between 14"-17" that's Short; somewhere between 19"-22" that's Long.

Beyond that, I'd check to make sure you're achieving full throttle. You can do this with the motor off, just shift to Fwd and advance the throttle. Make sure the Timer Base (under the flywheel, the flat round part you see with articulated linkage coming off of it fwd of the switchbox) is moving smoothly with throttle, and the carb is opening up all the way.

But I'm thinkin' it might be the Short vs. Long issue. Unfortunately not an easy way to make your motor shorter unless you find an entire S/S exhaust tower and also change the driveshaft.

It might be easier to build the transom up higher but that imposes additional stresses on the hull and you'd have to be very careful in doing that.

A pic of the boat/motor would help, then it'll be very evident what you've got. A view of the transom taken from lower unit height would be perfect.

HTH.........ed

Re: Mariner 30 - A bit slow or not?

Hi, thanks for the information, it is definately a long shaft engine on a short shaft boat. I previously had a long shaft '82 Johnson 25 on the back but the gearbox broke so I thought I'd get a newer engine, thing is, the Johnson has a smaller prop (not a thru-prop) and it seemed faster. I'm sure I'm hitting full throttle with the Mariner as there is a very slight notch on the throttle mechanism for full throttle on the engine. The boat seems very quick as in acceleration which makes me think that the prop is the wrong pitch, I can't really find out the correct one as I haven't got a serial number for the engine. How do I go about checking to see if the prop pitch is correct?

+ Dou you think some hydrofoils will help?

Re: Mariner 30 - A bit slow or not?

A hydrofoil would probably make it worse. The foil would be totally submerged in the water, the additional drag would slow the boat down even more.

Typically, if the setup is right, the hydrofoil is virtually out of the water when the boat's on plane. Foils are really meant only as planing aids, they might provide a bit of stability in turns but that's about it.

Prop wise, if the motor sounds like it's really winding out it might need a prop with more pitch. Of course a tach would be nice!

This would work:

http://www.tinytach.com/tinytach/gasoline.php

Probably a pitch increase of 2" would make a big diff.

If you can find any numbers stamped into the body of the prop, the last # is usually the pitch; something like "########-13" where 13 is the pitch.

Otherwise you may find numbers in the hub of the prop, where the prop nut tightens down on. Probably have to pull the prop to see if there's anything there. More likely are #'s on the hub.

Failing that, if you have a local prop shop they could put the prop on a pitch block or otherwise measure it out to determine the pitch.

Here's a few resources for looking up stuff for your motor. You can even poke around the Yamaha parts catalog and see if you find a model that's strikingly like yours.

http://www.autorepairmanuals.biz/site/573683/page/599222

http://www.maxrules.com/wireindex.html

http://www.boats.net/parts/search/Yamaha/Outboard/index.html