1150 Link & Sync Question

[jimmbo]

The optimum Trim angle for speed is just below where the boat begins to Porpoise, Generally the fast you go, the higher you can trim. However there are times when you will be running at Trim setting other than that. Running with the Waves, you might want to Trim Out more, while running in to the waves, some boats do better trimmed in, while others, trimmed out. Running at speed, trimmed in Too Much, can create an unsafe condition where, with the Bow digging in too much, can become a Pivot Point when you try making a Turn, and can cause the boat to Flip.
Trimming out too far allows Air to get to the Prop, and loss of Boat speed, with an increase in RPM. Some Props do better than others and can retain the Grip on the Water
As you trim an engine, your will feel a difference in the Steering. Trimmed in the Boat will want to turn to Starboard, Trimmed out, it will want to go to Port. Running Flat out Trimmed out, a sudden drop in Power will have the boat lurching to Port.

 

[jakec]

Ok had the boat out again today. Here are my notes.

Fully trimmed down I was getting about 29mph and a lot of spray. If I trim up just barely (very short button press) the speed increases to about 30mph. and spray goes down maybe 25%. As I trim up the speed increases to a maximum stable cruising speed of about 33mph. However at that point it's susceptible to porpoising if you hit even a very small ripple in the water's surface. Anything above the 33mph trim point I am porpoising like crazy.

So I settled in at that barely trimmed position and about 30 mph. I have a video to show the spray. it's pretty extreme in my opinion.

Video

In all I did a straight run of about 12 miles and then back so around 25 miles total for the day. To my surprise I used about 65% of my 15 gallon tank. So I estimate about 2.5mpg while on plane at about 30mph. Definitely a gas guzzler.

Finally when we returned to the harbor I was not able to put the engine in forward/reverse at idle speed (docking) without killing it. So even though it was fine last week, after a hard run I think it needs a higher idle to be able to move around at docking speeds. So next time out I will be raising the idle again.

 

[jakec]

In the video you can see it's more severe on the port side. You can see a solid stream hitting the aluminum corner trim. But it is also spraying evenly/less severe across the whole transom. You can see a softer vertical spray on the starboard side.

 

[jimmbo]

I suspect some of that is from the rounded Edge of the Transom. But the engine is bit low as well.
With a lot of effort. you could Fill-in/Build up the Rounded Area with some Resin saturated Fiberglass Chop, and with some grinding sanding end up with a nice Abrupt Edge, that the Water isn't trying to stick to
It would be nice if you had shown the difference as the engine was trimmed out.
I would have trimmed it to where it was close to porpoising, and been running a little faster. If you back off the throttle a bit, about 20%, the speed will drop a couple of MPH, but the fuel consumption will drop by a much greater Amount. It has been 25 years since I had a 115hp merc, and I remember it would drain a 5gal(Imperial) tank in about 30 minutes at WOT. But if I reduced the Throttle a bit, it ran over an hour on the same amount of Gas.

 

[Chris1956]

2.5MPG s not bad for a 2 cycle motor of that HP. My '77 Merc 1500 on my 16 foot speedboat burned 6 Gal in 20 min, at full throttle, with a heavily loaded boat @ about 50MPH. What length boat and what prop pitch do you have?

Unfortunately porpoising has a lot to do with the design of the hull. If you put a straight edge on the hull across keel to transom, is the hull flat? How about along the strakes?

Motor looks to be a bit low on the transom. The PTT brackets have a slip adjustment, so they can be raised a bit. You could put a 1X2 under the transom clamps. The only redrilling you may need is the lower transom clamps.

 

[jakec]

Jimmbo, it also occured to me last night that the spray seems to have gotten worse after removing the whale tale. If you view both videos from before and after, I think you will see it. So I may want to put it back on?

Also, I'm not at WOT, I'm running the engine at the lowest possible RPM before the drop in sound pitch and speed occurs (you can see in my first video when I throttle down the engine sound becomes lower pitch). So I would think I am at about 80% throttle currently. I would gladly trade some speed for fuel consumption, so can you explain more what I should do? Are you saying run in the low pitch sound range? I thought that meant I was lugging it.


Chris, unfortunately I didn't know what I was doing when I installed the outboard, so I offset the bolts in the slotted holes (top bolts are in bottom of slot and bottom bolts are in top of slot). I didn't consider the purpose of the slots at the time.

It is unfortunate but as long as I can run the boat this summer I don't mind. I basically built this entire boat this winter, so If I need to remove the engine and make some changes to the transom next winter that's fine. I would do it now but I want to fill and seal the old bolt holes correctly.

Here is the hull shape at the transom. Very shallow V with hard chines with a little negative turn/lip (not sure what to call that). Bow is deep V with lots of flare.

 

[Chris1956]

OK, well for that size boat, that 2.5MGP seems pretty good. The flatter bottom helps with efficiency. Make sure the tilt pin is on the lowest setting.

With a tach and a GPS you can maximize the efficiency. I would expect the whale tail to rob you of speed and efficiency, as it adds drag.

If you look over the transom at planning speed, is the antiventilation plate under water? I would expect so, and if so, do plan on raising it over the off season.

You could buy a cheap adjustable jackplate (~$150 new) and bolt that on to the transom and bolt the motor on to the jackplate. That will allow you to raise it up. The problem is that you will need to drill matching holes in the jackplate to fit your non-standard bolt pattern.

 

[jakec]

I have my tilt pin on the second position, which makes the outboard vertical (transom has a negative angle). Should I really lower it so the outboard will have a negative angle too?

 

[jimmbo]

The boat is little larger than I thought it would be.
Do you have a Tachometer? If yes, what is the maximum RPM the motor can Attain? If no, get one. A tach is essential in choosing a Prop that allows the engine to run in its recommended RPM Range at WOT, which on your engine is 4800-5300 rpm. The proper prop will load the engine so it is neither Lugging it, or or having it spin fast enough to start throwing pieces of Itself away.
The way the Throttle Linkage is designed, is to bring all the Spark Advance in first before the Carb opens very much, further movement of the Throttle, opens the Carbs. Once the engine is in the higher RPM range, pulling back on the Throttle will first close the Carbs, before the Timing is retarded. In this mode of operation, the RPMs do not drop Linear to the Throttle Lever. Most of the speed is maintained, but the engine burns less Fuel. I never adjusted my cruise Speed to a Particular Engine sound
As for the Whale Tail, I can't see it reducing spray, as it is at the Tail end of the AV Plate.

Most people either put the Tilt Pin in the hole closest to the Transom, or drop it in the water. Bringing the engine in closer, lifts the Stern of the boat up, pushing the Bow down. You said earlier that the Boat wants to Porpoise with very little Trim Up? You could try moving some items further forward

 

[jakec]

I was able to get the boat out again for the 4th of july weekend. We headed over across the puget sound to stay overnight at blake island. I haven't made any adjustments to the engine position or tilt. I did raise the idle a bit more (once again) so that it can now return back to idle after being warm / at WOT.

Getting on plane with 3 people and all of our camping gear was a little slower but I was able to use a lot more trim without porpoising. I think that the added weight helped. Although our gear wasn't that heavy (just sleeping bags etc) I had it all up in the cabin which may have added about 100 lbs. up there.

The only problem I had was the telltale stream because very weak very suddenly. I haven't been able to clear that up yet but I was able to boat the rest of the weekend and it was fine. The boat is moored at a marina now for the summer so I will climb on the back and try clearing the tell tale hole soon to see if it improves.

All in all I think I will most likely be done making adjustments for this year and revisit the transom and engine height in the winter.

As for a tach I do have one that I will hook up soon, but I suspect the gauge may be broken because it is showing 1k rpm when it is not plugged in. It's a generic mercury/quicksilver unit.

 

[Chris1956]

Some tachs will show the RPM when the engine was turned off. They usually zero when power is applied.

If you remove the cowling and pull off the telltale hose on the water jacket cover, the water should stream out of the engine at max volume for the elbow. If not, you have water pump issues.

 

[jakec]

Some tachs will show the RPM when the engine was turned off. They usually zero when power is applied.

If you remove the cowling and pull off the telltale hose on the water jacket cover, the water should stream out of the engine at max volume for the elbow. If not, you have water pump issues.

Yes, I was planning to pull the cowling and do that exactly. As well as poking the little hole with a paper clip or something.

The stream pressure went from 100% to very weak very suddenly. So I assume it must be an obstruction

 

[jakec]

Hey guys, unfortunately the beautiful 1150 that you helped me get going in the spring had a problem with the exhaust baffle and/or lower crank seal towards the end of this season. It was sucking water into the bottom 2 cylinders. Luckily I noticed the problem right away and go the boat out of the water and got the engine dried out and fogged, so it will be fixable.

However I had planned to one day go 4 stroke (maybe a couple years down the road) but it seems like now is the time. So the 1150 is off and I will sell it as is. Right now I'm going about correcting the problem with the radius at the bottom of the transom (going to add material there to get a sharp lip).

I'm also wondering if it's necessary to add 1" of material at the top of the transom, since I have seen plenty of photos where the outboard just overruns the top of the transom 1" or more. Right now I'm leaning toward leaving it.

As for my repower I have been looking at yamaha outboards as they are about 100 lbs. lighter than a honda of the same HP. I've been looking mainly at the f115 which weighs 375, only about 65 lbs. more than the mercury 1150. I was wondering if given the boats performance with the 1150, I should stick with 115hp? I've had multiple people tell me to go higher (150, 175, even 200). I don't want to overpower the boat. I was happy with my speed with the 115 (about 26-30 mph). My boat is quite heavy.

 

[racerone]

How high is the transom on this boat ??

 

[jakec]

It is a 20" transom. However when I built it I didn't take into account the angle, so the planar surface is 20", but it's actual height is less than that, more like 19". So when I plopped the 1150 down on it, the engine was about 1.5" too low.

 

[merc850]

The hull looks like a displacement type, a V type hull will attain a higher speed as it rises up out of the water; so that could be an issue. "generic mercury/quicksilver unit" is it an alternator driven or switchbox one?

 

[jakec]

It is a planing hull. not sure what you mean about the "generic mercury/quicksilver unit" ?

 

[racerone]

Looks like an easy to plane , near flat bottom to me.----And decals show the motor to be a 76 or 77 model.-----Those are distrubutor motors.

 

[jakec]

Near flat at the back with a very deep V at the bow.

 

[racerone]

Most boats are a V at the bow.