Question for twin outboard guys

[Ramifications]

Thanks, Droptop
Debating going 100% resto back to original, or maybe make some changes.
The gray and light blue stripe inlaid in the gel are pretty thin, so I need to at least do some paint work on the gray areas. My old Exiter had the same blue hull, except the Exciter had silver metalflake in the light blue/gray area. Maybe do the gray in metal flake, like the exciter, or just give it an updated look, and respray the whole thing and add graphics...not sure. I have a soft spot for the 80's Checkmate look, and for a nice metal flake scheme, although I've never seen a Enforcer/Convicor with metalflake

Boat actually has a little bit of history. Was Inland Marines, in RI, 1st Convincor. They were one of the kickoff Yamaha dealers in 84, so they put the biggest Yamaha's available on it, and used it as their demo boat for 2 years. Took it to Boston, and RI boat shows a couple times. All the guys there remember the boat, and can rattle off all sorts of facts and figures, as well as everyone who has owned it.

While I don't exactly remember the boat, when I saw it for sale, it seemed familiar. I grow up in RI, about 10 min from Inland Marine, and bought my 1st boat from them in '85/86, so I must have at least checked it out back then

Hopefully found why the starboard engine was making wasn't making as much power as the port. The TPS on both engines were way off. TPS on these old Yamis is one of two primary sensors that controls timing. Got them dead nuts matched at idle, and WOT, synced them, and adjusted rigging and to keep them as close as I could thru the full range. Hope to get out this weekend to see if that did it for the engines

The lower unit I though I had found was the wrong ratio, so still looking for a 1.85/1 RH lower.

BTW - I had an Exciter with the same color scheme

 

[knarloid]

Kris - I need to borrow your Choppers next time we meet up.

Anytime compadre!!

 

[70 ragtop]

I have the same hull as Jup - 2800SX. Same as the 251, but stretched 3'. This is my first real season with the boat. I ran it one time December last year with twin 2.4 200's and 28" of setback with them spinning in with 26p Choppers. The porpoise was almost unmanageable... I had to put the K planes down about 75% to make it manageable under 50 mph. The engines were set at 19" centers and I had basically no ability to use forward and reverse to maneuver the boat around the dock.

I repowered this season with twin Verado 300's and it is a totally different boat. Depending on the load in the boat, I don't need the tabs. When I have a few hundred extra pounds in the back, I need the tabs to manage to porpoise, but it only requires a little tab. My current setup is 6" setback, 27" centers (as close as I can mount them without touching), spinning out, 2.5" below the bottom and still playing with props and height.

I also put 200 lbs of sand in the bow since I do not have a finished cabin yet. I have run choppers and they work and have produced the highest speed so far (78 mph) but lower speeds and handling isn't that good. I have tried four blade hydromotives, bravo 1's and four blade BBlade Blasters. I had the best overall performance with the Bravo 1's. I will be installing a set of Bravo 1's and raising the engines another inch in the next week or so.

This hull is definitely a drivers boat. With the narrow beam and deep V bottom, they are sensitive to tabs and weight distribution. Try to even the load from port to starboard and and make minor adjustments to the tabs and let the boat react for a couple seconds before any other adjustments. It will take some getting use to, but you will find the comfort zone!

I would also like to attend the CT River Run this year! Droptop - you can borrow my 26p Choppers anytime.

Great info, Thanks!
I've only had the boat out twice, and making changes after each time to get things sorted. I hope I've got the engine gremlins sorted, and they're matched now. Already put lowers on with props turning in. Will swap them to out after the next test hop and see which the boat likes best.

Boat was cruising nice in the 40s, but it needed a bit of tab. Just like you said, small tweaks and wait for it.
I didn't really feel a big difference in the 50s, but I still had some down tab. It would still porpoise if I brought them up too much. I dropped the hammer a couple times, and you could feel it wanting to go...even with one engine not really right, and both props turning RH. My daughter saw 63 on the GPS as the tabs were coming up, but she stopped looking when the bow started getting light. Seemed odd the bow got so light with the engines almost all the way in. Think I'll go ahead and throw some sand up front before next time out as well

I'm looking forward to getting it back out and getting some seat time.

 

[70 ragtop]

BTW - I had an Exciter with the same color scheme

Nice! that was a great boat.

 

[70 ragtop]

So got the boat out twice today with mixed results, first run was props turning in, second props turning out.

In and effort to "shotgun" nose balast, I threw 500lbs in the nose, in front of the mirror
Naturally the proposing was dampened, boat felt OK, but heavy. Speed was down, performance was underwhelming, but boat felt very solid

I spend a bit of time setting throttle position sensors, and matching the rigging in the shop, and was surprised to see a 600 RPM split. Here's the odd part, the engine that was running 400 RPM higher last time, was now the slower engine

I didn't bring a meter with me, but did a little on the water tweaking anyways, couldn't get any positive change from that engine.

Swapped drives, now turning out, reset TPS to correct for the blind tweaking I did, and put it back in the water. The RPM split moved to the other side. Now I did triple check that the gear ratios matched.
Running just one engine, the RH prop moves the boat pretty good and loads the engine. The LH prop seems to be slipping pretty bad.

I really need to get some nose cones, push them back away from transom, and lift them a little. All things I wanted to do over the winter, but why the LH prop slips so bad compared to the RH eludes me....
These props are all serialized, you would think they were matched. Looking at them, I don't see any obvious differences.

Now for porpoise, boat handled better with props turning out. At this point, started moving ballast around. At 200 lbs in the nose, was having to put more tab down, and it was right on the edge of starting to porpoise. Any change in water, would set off the bouncing.
I tried a throttle bump, I hammered it, trimmed them out and back in, didn't help. A slight turn would dampen it, but it would come right back once straight again. More tab smoothed it out, and it was fine.
At 250, ride was really nice at all speeds with very little tab, hitting a wave didn't set it off. More weight was smoother, but at 250, it didn't feel heavy, and it wasn't bouncing around.

Still need to keep engines trimmed in, can only add very little trim. More engine trim needs more tab to keep it from porpoising, and I run out of tab quick, plus they are just dragging. Longer tabs might solve that problem

We saw 63 with the two RH 1.73 lowers on it. That was with one engine not running quite right, and had to get out of it while it was still accelerating when it started bouncing. Figured I would loose 4-5 MPH going to the 1.85 cases, but 13+. I didn't see 50 all day, which is a huge problem. Got the be that prop slipping

Looking at slip calculators, looks like LH slip is 35%, RH is 28%, just based on RPMs. With the two RH 1.73 cases it looks like around 22% slip with the same RH prop

Any thoughts?
Any ideas on how to lower prop slip, or why LH seems to be slipping so much?

 

[DropTop5.0]

I'm not going to be too much help but I'll give you a few things to think about. Sammie told me a while back that there is no such thing as a matched pair of props. And what he meant by that if I remember right is that the prop builders work all day long on right props and every once in a while they do a left hand prop. So Joe Blow could have done your right one and Susie Q could have done your left one and they are not going to have the same skill set either. So... Can you try another set of props?

I tried one set of Hoss chopper style props and had 10% slip and went to a Merc Chopper (worked) and had 22% slip. Props look good and clean to me though so why did my slip go up by 12%?

Are there any stamps on your props indicating they've been worked?

As far as cones go it is my understanding they do not help in anyway until after 80 mph. If your having water pressure issue, there are other ways to address that other than cones.

And lastly pushing the motors back probably isn't going to help with the porpoise. Jackplates will help you get the motors up and down of course but I doubt its going to improve porpoise if that is your goal for moving them back. Right now I have my the prop shaft about three inches below the hull. I just went out and measured by taking a yardstick and pushing it against the hull and measuring from the stick to the prop shaft.

 

[70 ragtop]

I'm not going to be too much help but I'll give you a few things to think about. Sammie told me a while back that there is no such thing as a matched pair of props. And what he meant by that if I remember right is that the prop builders work all day long on right props and every once in a while they do a left hand prop. So Joe Blow could have done your right one and Susie Q could have done your left one and they are not going to have the same skill set either. So... Can you try another set of props?

I tried one set of Hoss chopper style props and had 10% slip and went to a Merc Chopper (worked) and had 22% slip. Props look good and clean to me though so why did my slip go up by 12%?

Are there any stamps on your props indicating they've been worked?

As far as cones go it is my understanding they do not help in anyway until after 80 mph. If your having water pressure issue, there are other ways to address that other than cones.

And lastly pushing the motors back probably isn't going to help with the porpoise. Jackplates will help you get the motors up and down of course but I doubt its going to improve porpoise if that is your goal for moving them back. Right now I have my the prop shaft about three inches below the hull. I just went out and measured by taking a yardstick and pushing it against the hull and measuring from the stick to the prop shaft.

Makes sense on props not being matched, that's got to be the issue with the LH prop. I'm going to try one more test run and stick the other RH 1.85 case on it, and do some swapping around

Right now I'm chasing engine tuning issues, using props that I'm not really sure are matched. Can't really count on a RH prop on the left side of the boat loading the engine the same as a RH prop on the RH side of the boat. If they didn't have the V of the boat in the way, yes, but that's not the case

Cones would be for water pressure. Thinking I had to lower them to get good water pressure, but not enough to to get them below the boat into clean water, wouldn't want them that low anyways. Being trimmed all the way in has got to be putting props in a bit of turbulant water, and making it hard for them to get a good bit
Moving them back from the transom would help get props into cleaner water, and may very help the water pressure issue without needing cones. Moving them back would most likely make the porpoise worse

Talked with the folks at Hydromotive today. After doing some testing on the RH props to make sure they are the same, or at least confirm some speed vs RPM numbers for each prop on each side, going to send one to them so they can confirm what pitch they really are, and go from there.

 

[70 ragtop]

Talking about the porpoising with the guy at Hydromotive, he also mentioned a hook in the hull, and also recommended using a 8" straight edge. I asked how much of a high or low spot in hull would affect the boat, and was pretty surprised when he said a 1/16" would do it, 1/8 would be bad.

I would like to get engines running the best I can for this season, and plan to pull them and go thru them over the winter. Not really looking to buy new props now, especially when we're talking $1300. If I can find a good set of Bravo 1s, Quad 4s, or even a pair of Laser 2, at least I would have something to compare to these props.

Either way, going to wait until I pull the engines for the winter refreshing to do anything on the bottom. Sure would be nice to flip it, gonna suck looooong boarding it over my head

 

[DropTop5.0]

I have a set of hydromotives for sale. I liked them I just didn't have quite enough power to spin them correctly. http://washingtondc.craigslist.org/nva/bpo/5717104559.html

 

[demag67]

If you still end up needing some help pm me and i can give you my number. I did the work on droptops boat and may be able to help you out a little bit. I am no way an expert but between droptops boat and mine and have done a lot of work and a lot of trial with the two twin outboard checkmates.

 

[DropTop5.0]

When Bruce got done with my boat, we ran 73 GPS first run out.

 

[70 ragtop]

I have a set of hydromotives for sale. I liked them I just didn't have quite enough power to spin them correctly. http://washingtondc.craigslist.org/nva/bpo/5717104559.html

Thanks, I don't think I will either, but I would love to try them. What RPM were you turning them, and what speed?

 

[70 ragtop]

If you still end up needing some help pm me and i can give you my number. I did the work on droptops boat and may be able to help you out a little bit. I am no way an expert but between droptops boat and mine and have done a lot of work and a lot of trial with the two twin outboard checkmates.

Thanks, appreciate the offer!! Read thru thread Droptop posted, very impressed. Never seen the outside of a transom cut off like that, you guys did a great job
Whoever did my transom cut the splashwell out, and did an awful job repairing it. Fixing it is part of my winter plans, or once the engines come off

 

[70 ragtop]

When Bruce got done with my boat, we ran 73 GPS first run out.

I would be happy with that

 

[70 ragtop]

Picked up a set of well used Mirage 14.5x25 props today for cheap. Slapped them on and took it out. The difference is night and day.
Boat cruises at 40MPH at 3500 RPM, thats 11% slip. WOT RPMs were a little low, which goes along with the Mirage having a little bigger blade for bigger OB and IO. This pair pushed a 38 Formula, which is a whole lot more boat!

I was finally able to make progress getting it to move like it should. Almost full tabs down, full throttle, trim the engines, then bring tabs up. Boat got up on the pad and was accelerating hard as we approached the dam and had to stop. Was REALLY low on gas at this point ( engine sputtered), so took it back to the ramp.

Wasn't able to just go full throttle and bring the tabs up as it would start porpoising. Was doing mid 50s when it started bouncing real bad at full throttle, and the RPMs were low, only about 5000 WOT. But trim the engines up, then bring the tabs up seems to be the trick. Boat was rock solid, and accelerating. Wasn't expecting it to settle down so nicely and didn't have GPS out, but speedo was was showing low 60s

These are old Mirage props, without the heavy cup of the plus, nor the ventilation holes. I need to find the right thrust washers if I want to keep running them as they are solid hub, and the thrust washer pilot diameter is different than what I have

Honestly, I think I need a set of Laser 25s. Smaller blade to get the RPMs up, same pitch should let the engines unload

Starting to like this boat

 

[DropTop5.0]

That's great to hear! So all the slipping with the port motor was all about the prop? Is that right?

Try and find a pair of choppers and see how they work on your hull.

 

[70 ragtop]

That's great to hear! So all the slipping with the port motor was all about the prop? Is that right?

Try and find a pair of choppers and see how they work on your hull.

Seems to be

How do you get your boat up to speed? I've never owner a boat that I need to trim the engines up while dragging the tabs, then bring the tabs up. Seems odd

 

[DropTop5.0]

I have my planes set about 1 click down from straight (parallel) with the boat and that's where they like to run on my hull to prevent any porpoise. I trim the motors down all the way and just hammer the throttles. If it starts cavitating I back off until the props bite. The over the hub props (choppers) cavitate much less than the thru hub props for me.

When I'm really heavy I'd set the tabs down further.

Last year my transom had a bunch of black around many of the holes. Do you have anything like this inside your boat?

 

[70 ragtop]

I have my planes set about 1 click down from straight (parallel) with the boat and that's where they like to run on my hull to prevent any porpoise. I trim the motors down all the way and just hammer the throttles. If it starts cavitating I back off until the props bite. The over the hub props (choppers) cavitate much less than the thru hub props for me.

When I'm really heavy I'd set the tabs down further.

Last year my transom had a bunch of black around many of the holes. Do you have anything like this inside your boat?

No, but the transom has already been redone, and seems ready solid. I do need to redo the glass/bodywork in the splash well, as the finish work is pretty bad. They ended up making transom fatter than stock, and adding taller knees that tie in the whole splash well to the transom, and I assume they a glassed everything into the stringers under the floors ( at least I hope they did). Can see floors have been replaced up to the step in the bow, so hopefully they addressed stingers and foam as well.....but you never know

I bet if I had longer tabs like yours, they would control the porpoising getting up to speed, without dragging so much.

Ordered a pair of 6" jackplates this AM.Tape measure must have malfunctioned when they were drilling mount holes, as one engine is just a touch lower than the other. Will make it a lot easy to start tweaking height, and a little setback may help on the high end. Wanted to go 10", but afraid it would really kill the midrange cruising. Wife's not really big on speed, or bouncing....go figure

 

[70 ragtop]

Installed the jackplates, and took it out yesterday. Ended up raising them a couple inches on the water until it was happy.

RPMs with the Mirage props is right at 5500-5600, speed (per speedo) is mid 60s, and the boat feels great.

Mid propose is easily manageable with tabs, MUCH better than the first couple times we took it out with the semi cleavers on it

Blocked the top half of the inboard water pickup on the starboard engine (think that area's sucking air)and that engine was running 5 PSI more pressure than the port, and in general, water pressure was better than it has been.

Getting them back off the transom really seems to help. wishing I had gone with 8" or even 10" plates now

The Mirage props are not the right props for this setup and top end, but for now they are okay. The steering has a lot of play in it, and just one hyd cylinder. Boat was just on the edge of a little chine walk yesterday, so no need to go any faster until I upgrade steering