For a few reasons, one becuase I think I need to buy a different prop and the majority of the people on this site have been saying that before you do that you should ensure your motor height is correct for the boat. <br /><br />Another because it has a tendency to porpoise at WOT when you attempt to trim up to get more of the boat out of the water. It will also do it if your cruisng along at 30+ mph and the current suddenly changes (as a result of being trimmed down too far for the amount of throttle applied - most of the time a bit more throttle corrects this but not always).<br /><br />The last reason is because it seems to have quite a bit of torque steer often requiring two hands on the steering wheel if you want to turn left (I was wondering if rasing the motor up would lessen it). <br /><br />Here's a bit of background of what I've been through so far:<br /><br />When I bought the boat the prop that came with it is a 13.75 x 21p SS 4-blade Trophy Plus. It seems like this is too much prop for the boat/motor as I found it would only rev 4400 rpm @ WOT and top out at 39 mph (not sure how or when it ended up on the motor). Out of the hole the nose would shoot in the air and the motor would slowly build up rpms, taking quite a while to get on plane. While on plane it didn't feel that responsive especially after 3/4 throttle.<br /><br />I had a chance to try a 13 x 19 3-blade aluminum and it woke the boat up. Planes relatively easy and runs 5200 rpm @ WOT, 43 mph. The spec says it should be 5000 to 5500 rpm however most have told me to run it at 5400 which means I'm down about 200 rpm. <br /><br />I also tried a 13.25 x 20p SS 3-blade Laser II but found it very revvy until you got on plane. Like the Trophy Plus it would drive along with the nose in the air except there was no probelm buiding rpms as it would quickly ramp up to 4800 rpm and stay there until it slowly gathered enough momentum to get over the "hump" and get on plane (even if you rolled the throttle on slowly). Once on plane it cruised at similiar rpms as the 13 x 19 aluminum but was noticeably more revvy when you suddenly opened up the throttle more (both props would run 4000 rpm at 30 mph).Top speed was 44 mph @ 5300 rpm.<br /><br />So now I'm thinking a 13.25 x 17p 3-blade aluminum would be the way to go to gain 200 rpm but I'm wondering if I should try rasing my motor before I go out and buy one (I don't know anyone who has one I can try). The problem is I don't want to cut the capping on the transom to do so unless I'm sure I won't be switching it back. <br /><br />Maybe the handling characteristics etc. are because of the type of hull. I uploaded a picture of it along with one of the three props I tried incase they may help.<br /><br /> Boat pics
The aluminum edging/capping that over laps the top of the transom makes that part of the transome thicker. Right now the top mounting hole of the motor bracket is just below it and flush against the fiberglass of the transom. If I was to raise it up one hole it will overlap the edge of the capping and the bracket would not be square against the back of the transom (the metal above the top hole of the bracket curves slightly backwards therefore clearing the capping). I wouldn't want to go a head and cut it away only to find out that I need to lower my motor back down.
Thanks, right now the A/V plate is level with the keel. For some reason there was no trimfin on the boat when I bought the boat but I put one on. I've tried adjusting it a couple of times but it sounds like the wrong way (I turned the trailing edge to the left thinking it would make it go that way). I also cut a notch out of it (as a dealer told me to do) as there was only about 1/8" of clearance with the 13.75 x 21p Trophy Plus prop installed. Maybe this has something to do with it?<br /> Trim Fin and A/V plate level with keel <br /><br />When you say watch for water pressure do you mean make sure the stream coming out the back doesn't weaken or become intermittant (I don't have a water pressure gauge)?<br /><br />I like the idea of shimming the motor plate with an aluminum plate so it can be put back how it was if it doesn't improve the situation. I should probably mention that all my testing has been with only two people in the boat. I was thinking that before I try rasiing the motor I should load the boat up with 4-6 people to see how it reacts (I still have the 13 x19p aluminum prop to use for now).
I wasn't going to move the bolt, it's the raising of the motor bracket that will cause the top of it to contact the metal capping. I posted a pic of the other side to see if that helps or not. Right above the top hole in the bracket the bracket starts to recede backwards slightly. If there was no capping on the transom this part would not be touching the fiberglass at the top.<br /><br /> Motor bracket
I think I like SoLittle's idea of placing a aluminum plate behind the bracket to shim it out so it will clear. That is unless anyone can see a problem with that???<br /><br />Since I have to remove all four bolts to re-locate them in the mount I'm wondering if I should use a floor jack under the bottom of the motor along with a strap supported from the ceiling to raise it (I have a chain hoist suspended from the ceiling of my garage that I was thinking of using).
How much larger than the motor bracket face should I make the plate (is it benificial to make it bigger?)? I take it I will have to completely remove the motor so I can mark the holes I need to drill in the plate? <br /><br />Is it normal for the top mounting bolts to be one way and the bottom to be the other (the nut is on the outside of the transom for the top bolts and on the inside for the bottom)?
I posted a pic of the trim tab before I cut it to give an idea of how little clearance there was with the Trophy Plus prop installed (the pic with the tab cut if with the laser II prop installed which has more clearance). Maybe that's why the previous owner removed it???<br /><br /> Trib tab before I cut it
If I'm running at 5200 rpm with the 13 x 19p alum. prop how much can I expect the rpms to increase by raising the motor up by one hole (right now it runs about 200 rpm low)? Is there a good chance a 13.25 x 17p would overrev if the motor was raised (at the current motor height, from what I understand my rpms would increase by about 200 rpm putting it right where it should be at 5400)?
I haven't tried rasing my motor yet but I had the chance to try two more props, a 13.25 x 17p alum. Merc prop and a 13 x 17p K-2 black SS Yamaha prop. <br /><br />The Merc prop performed similiar to the 13 x 19p Merc prop but it was a bit more revvy near the top and it made the nose ride a bit higher when cruising at non-planing speeds. It gets up to 30 mph pretty quick but the speedo climbs noticeably slower after that. Top speed was 41-42 mph @ 5400 rpm so it's running where I was told it should be but it appears to be a bit slower in the midrange and top end (two people in the boat as with all other testing except the buddy with me this time is about 50 lbs heavier than my brother who was with me when I got 43 mph @ 5200 rpm with the 19 pitch).<br /><br />When I tried the 13 x 17p SS Yamaha prop the first things I noticed was that the nose rode a lot lower when cruisng at non-planing speeds and that most of my torque steer was gone (I was quiet amazed at how much easier I could turn left regardless of trim position, I really like that). The boat still has a tendency to porpoise if you get carried away with the trim but it seems to come out of it a bit better if you catch it in time (otherwise you have to really back off the throttle to get it to stop).<br /><br />The prop seemed to perform real well at most speeds but like with the 17 pitch Merc prop it was a slower climb after 30 mph (from 35 mph and up it's probably the slowest of the three, it almost felt like it could use a bit more gear but it wouldn't over rev until you held it WOT and bumped the trim up until it got close to porpoising). Top speed was 40-41 mph at 5600-5700 rpm which is a bit on the high side (with the same buddy in the boat).Cruising at 30 mph the Yamaha prop revs at 4600 rpm compared to 4000 rpm with the 19 pitch Merc (I forgot to check the 30 mph rpms with the 17 pitch Merc prop). Now it's got me wondering what a 19 pitch SS Yamaha prop would do or even a regular alumin. 17 or 19 pitch Yamaha prop (I'm not sure if my motor has enough power to really benefit from a SS prop). <br /><br />I plan to do a bit more testing with more people in the boat to see how much that effects WOT rpms. From a handling and driveability point of view the Yamaha wins hands down but I think the motor needs to be loaded a bit more at the top. It also seems like both aluminum Merc props may benefit form raising the motor but the Yamaha one may not.
I tried putting the trailing edge of the trim tab to the right instead of th left but didn't notice much difference. Could this be because of the notch I cut out of it (it no longer has a pointed leading edge)? <br /><br />As I mentioned in my last post the Yamaha prop I tried greatly reduced the amount of torque steer I was getting.
<br />Note: Any boat dealer that would tell you to cut out a trim tab for clearance, surely does not know much and I would stay as far away from him as possible!!!!!!
