Motor/hull set up questions (with pics and vids)

[fakirone]

Okay, so my 1995 Mercury 25hp has been rebuilt and it's running great. I clocked 31 with a lightly loaded boat (all three batteries, 2 deep cycle Optimas and one for the starter), two cases of beer (very important), and a heavy bag on board. Since then, I got my Beavertail pods welded on and bolted up my prop saver. Today I went out and started playing with my weight distribution and to check planing and speed with the additions.

Today with a full 6 gallon tank and an extra deep cycle for weight my top speed was 26 mph, which I feel is pretty great considering how much drag the prop saver adds to the equation. I moved the two Optimas to the rear deck by the transom where I planning on carving out some storage and the boat sat perfect at rest, but did get some slight porpoising while at full clip. I almost always fish with another person so I am sure that this will be gone with the added person on board.

[youtube]vkLRN7o4sP0[/youtube]

I also ran it with the batteries back up in the forward location that they were in originally. No porpoising, but it was a little slower, 25 mph, but that may have been more due to water and weather conditions and it was starting to get a little windy and raining.

[youtube]BuhUdfloOv8[/youtube]

Anyways, to my set up question. Currently the cavitation plate is almost dead level with the bottom on the boat as you can see in the picture (the PVC pipe is running straight from the bottom of the hull), but I seem to be getting a lot of splashing from the motor and I was wondering if you guys think that I should get a jack plate and raise the motor. Or am I just thinking to hard and this is basically how it should be?

 

[stevesecotec02]

It lools ok to me. I have the same motor except mine says mariner on it and almost the same boat mime is just a mod vee with the 20" transom and I found I get best performance from running on the fourth pin hole from bottom. It lifts front pretty food at first but planes out quick and rpms drop down nicely at full throttle.

 

[fakirone]

stevesecotec02 » 21 Jul 2014, 03:49[/url]"]It lools ok to me. I have the same motor except mine says mariner on it and almost the same boat mime is just a mod vee with the 20" transom and I found I get best performance from running on the fourth pin hole from bottom. It lifts front pretty food at first but planes out quick and rpms drop down nicely at full throttle.

That's the one thing that I didn't mess with while doing laps on the river. My bracket has 5 holes and I am 4 out from the hull, second from the furthest.
I guess I'll grab some weights from my gym and put another 200lbs up front (second fisherman) and head back to the river to play with the settings. I have a piece of 2"x3/4" aluminum bar stock that I can use as a spacer across the transom. I guess I'll stick that in there to see what that does too.
Hopefully I can make it to the water tomorrow morning.

 

[Natedog57]

Regarding motor height... I think you're very close to where you need to be. I'd try adding a 1" - 1.5" spacer (over the transom, under engine bracket) to raise the cav plate slightly above the bottom of the hull. I've been able to have the cav plate 1.5" above the hull, then on another boat that was to high, it needed to be "in line" like yours is now.

Regarding trim settings... the farther back raises bow running height, and moving forward(closer to the transom) lowers the bow. I always tried to set my motors up so the bow might porpoise slightly with a very light load, but then be fine with a heavy load... or you can change settings depending on how you're going to run the boat on any given day. Generally speaking, farther back will take longer to plane, but have better top end speed (as long as it doesn't porpoise).

With all the batteries you have I don't think you'll have issues with porpoising, I'm guessing that if it's too far back it will just be very slow to plane out.

Congrats on that Merc, I've got one and it's a sweet little motor.

 

[Stumpalump]

The baseline of 31 was good. I like to see what one change at a time does. Pull off that prop guard and load the boat like it was when you saw 31 to see what the extensions did. Try to get it to run like it used to before you add more weight and drag. You may find the extensions push more water toward the prop and you can raise the engine. Same with the extra weight. Once you get it maxed out with height and trim and your still not gaining speed then you can look at RPM and prop pitch.

 

[fakirone]

Today I ran with my son (110lbs), both Optima D31M batteries (60lbs a piece), a Xtreme X2-18L motorcycle battery for the starter (about 15lbs), a ProMariner ProSport 20 (11lbs) and a Jeep wheel for load (about 45lbs).
I started the day with a 3/4" flat bar of aluminum under the motor and trimmed all the way out. I couldn't even get on plane there, so I took the trim out a hole at a time until I could hook up. I didn't hook up until I was second to closest to the transom, but by then I was digging the bow in so bad top speed was 19, so out came the aluminum bar.
Back with the motor flat (anti ventilation plate even with the bottom on the boat) I started again trimmed all the way out with the same load. I got up on plane but was definitely hitting spots where the prop would let go, one hole down and I was good. So four holes out from the transom, second to furthest out seems to be the ticket.
With this load I got 27 MPH without the prop saver and a steady 25 flashing into 26 here and there with the guard. For a mile and half per hour I'll definitely keep the prop saver on. I think that I will try a jack plate and see if the set back will let me raise the motor some more, but for now I am done. I have been looking for a smaller adjustable jack plate that doesn't have a ton of set back, but I haven't been able to find one. I might just have to fab one up.

Today's run.

[youtube]SMvLBonaxWE[/youtube]

 

[fakirone]

Stumpalump » 22 Jul 2014, 12:38[/url]"]The baseline of 31 was good. I like to see what one change at a time does. Pull off that prop guard and load the boat like it was when you saw 31 to see what the extensions did. Try to get it to run like it used to before you add more weight and drag. You may find the extensions push more water toward the prop and you can raise the engine. Same with the extra weight. Once you get it maxed out with height and trim and your still not gaining speed then you can look at RPM and prop pitch.

Yeah, I do need to go ahead and invest in a tach. :|

 

[fakirone]

Stumpalump » 22 Jul 2014, 12:38[/url]"]The baseline of 31 was good. I like to see what one change at a time does. Pull off that prop guard and load the boat like it was when you saw 31 to see what the extensions did. Try to get it to run like it used to before you add more weight and drag. You may find the extensions push more water toward the prop and you can raise the engine. Same with the extra weight. Once you get it maxed out with height and trim and your still not gaining speed then you can look at RPM and prop pitch.

Also, I have a Mercury 48 19640a40 prop (10 3/8" 13 pitch) on it now and a Solas 10.1" 13 pitch in the garage. It doesn't seem like there would be much difference between the two, right?

 

[flatboat]

Idealy the cavitation plate should be running very close to the same plane as the boat bottom . ,,,i'm not saying it should be the same height . Some boats ,with their hull design ,allow you to raise your motor a little higher than others . The angle of the transoms differ from boat to boat, ALL setup work is trial and error . on some I have had to put rubber hose over the pin to get 'half a hole ' on the trim . If you decide to put a jack plate on it you should be able to raise it a little more . As far as those two props , always try all you can, stainless and aluminum DO NOT run the same . every prop runs a little different especially being different manufacturers ,In theory a 13 should run like every 13 but that ain't tru ! With a small motor tiny things add up to less speed or more speed . there's always a small tweak that can be made to a prop to add or take away rpms ,to hit the sweet spot so to speak . As suggested earlier its hard to dial in without a tack. . a GOOD prop guy can put your rpms anywhere you want them
good luck at least you are in a boat .......'investigating performance issues ' that's got be worth a little sanity rejuvenation !

 

[fakirone]

flatboat » 23 Jul 2014, 22:43[/url]"]Idealy the cavitation plate should be running very close to the same plane as the boat bottom . ,,,i'm not saying it should be the same height . Some boats ,with their hull design ,allow you to raise your motor a little higher than others . The angle of the transoms differ from boat to boat, ALL setup work is trial and error . on some I have had to put rubber hose over the pin to get 'half a hole ' on the trim . If you decide to put a jack plate on it you should be able to raise it a little more . As far as those two props , always try all you can, stainless and aluminum DO NOT run the same . every prop runs a little different especially being different manufacturers ,In theory a 13 should run like every 13 but that ain't tru ! With a small motor tiny things add up to less speed or more speed . there's always a small tweak that can be made to a prop to add or take away rpms ,to hit the sweet spot so to speak . As suggested earlier its hard to dial in without a tack. . a GOOD prop guy can put your rpms anywhere you want them
good luck at least you are in a boat .......'investigating performance issues ' that's got be worth a little sanity rejuvenation !

I am TERRIFIED to run a SS prop. I smack the hell out of my lower unit all the time (hence the prop saver) and would hate the repair bill on that one. I ordered a tiny tach (hope it works) so I should be able to get some RPM numbers in a couple days. Also, I am going to take my Solas in to get fixed, it was bent on fathers day when I whacked a log. When I get it back in I guess can compare the two.

Also, I happen to have two of the Mercury 48 19640a40 props, once I figure out if my boats runs better on the Solas or the Merc I will have one extra if anyone needs a prop.

 

[BigTerp]

fakirone » Today, 1:04 pm[/url]"] I ordered a tiny tach (hope it works) so I should be able to get some RPM numbers in a couple days. .

I have a tach very similar to the "tiny tach". Works great!!

 

[kofkorn]

fakirone » 20 Jul 2014, 22:49[/url]"]

Quick suggestion: Flip those bolts holding the prop saver on. Get the nuts out of the flow path and keep the nicely rounded carriage bolt heads there instead. Probably won't gain much, but it certainly won't hurt.

Good luck!

 

[fakirone]

BigTerp » 24 Jul 2014, 14:08[/url]"]

fakirone » Today, 1:04 pm[/url]"] I ordered a tiny tach (hope it works) so I should be able to get some RPM numbers in a couple days. .

I have a tach very similar to the "tiny tach". Works great!!

Good to hear!

kofkorn » 24 Jul 2014, 15:29[/url]"]

fakirone » 20 Jul 2014, 22:49[/url]"]

Quick suggestion: Flip those bolts holding the prop saver on. Get the nuts out of the flow path and keep the nicely rounded carriage bolt heads there instead. Probably won't gain much, but it certainly won't hurt.

Good luck!

Yeah, I actually did that right after I posted this because I noticed it in the picture. The bolts are hex head, but I am going to see if I can find some carriage bolts for it. Like you said, may not do much, but certainly won't hurt! Thanks for the advice.

 

[fakirone]

So I got my Tiny Tach last night, I am headed to Arkansas to fish the White River tomorrow early AM so on my way to drop my boat at my buddy's house (taking his truck) I threw the boat in the river to check her out. I was supposed to be at work so I was in a major hurry, but I wanted to get a baseline with the boat fully rigged but not loaded at all, just the one person, me.
Well I was pretty disappointed with the numbers. Wound up with a top speed of only 25, much less than I got the other day with a small load (31 mph then). I was turning 5360 rpm to get that speed. Same both up and down river. Bummer.

So I haul butt back to the ramp and start to load her up and I notice... I had left the choke on for the whole testing process.

Lame.

 

[fakirone]

I wound up moving the batteries back under the front of the far deck. The boat now sits perfectly level in the water when unloaded, but I start porpoising at about 24-25 MPH with only me in the boat. I NEVER take this thing out alone so I am going to have to get some weight up front and see how it runs.

 

[fakirone]

Oh, and my Tiny Tach is completely fogged up and unreadable. I guess I am going to have to unmount it and take it apart to be able to use it.