Tohatsu Nissan TLDI 50 hp prop selection

[myhuntfish]

I have a 1552 semi-v Alweld with Tohatsu 50 TLDI tiller. Boat empty hull weighs 350 lbs, have 6 gal gas tank and one batt in back, one batt in front and troll motor. I keep my anchor and cooler in front for weight distribution. Motor is mounted with cav plate about 1.5" above bottom of boat. No cavitation problems. I am getting about 35 mph on gps (with one,two or three people same speed just can get more trim angle) with factory 11" X 15" pitch alum prop. Factory prop seems a little low in top speed RPM. I tried a Powertech SCB 10.38" X 15" pitch SS prop and it killed my low end and became very weight sensitive but ran about 36-37 mph with a very light load(just me). I am exchanging this prop for a Powertech SCA 11" X 13" pitch prop in hopes of better overall performance (more thrust from larger diameter prop) and increased RPM. I am trying the Semi Cleaver style prop for stern lift in hopes of stopping the annoying porpoising issues. It porpoises terribly unless I have the fixed trim tabs bent down on the boat, but it sprays water everywhere- also annoying. Motor is a tiller so I have no tach. I tried a tiny tach but could not get it to work. It read all over the charts unless I was physically holding the red wire in place, then it would read correct. If anyone has suggestions on prop for this motor/boat setup or even a similar aluminum boat/motor set-up I would greatly appreciate it. Thanks

 

[pootnic]

Re: Tohatsu Nissan TLDI 50 hp prop selection

It seems your already in the ballpark.
I'm sure you don't want someone to say a 14 pitch...theres just too many varibles in the boats,plus the props.
A tach is the only way to fine tune...sorry.

 

[myhuntfish]

Re: Tohatsu Nissan TLDI 50 hp prop selection

It seems your already in the ballpark.
I'm sure you don't want someone to say a 14 pitch...theres just too many varibles in the boats,plus the props.
A tach is the only way to fine tune...sorry.

I understand. I am mainly curious on suggestions of blade style and diameter for this engine or similat on a short wide aluminum boat that is heavy in the stern such as my 1552 alweld semi-v

 

[myhuntfish]

Re: Tohatsu Nissan TLDI 50 hp prop selection

HELP! I have tried the 11x13 prop. No better. Installed a jack plate and smart tabs. Cav plate 2.5" above bottom of hull. No more speed. Also installed a tach and only getting 5000 rpm with this prop. I am having serious porpoising issues when trying to trim up unless the smart tabs are down. Them it plows with the smart tabs. I just can't understand why the rpms are so low with a 50 hp on a 1552 aluminum boat and only 13" pitch? Please help! I am so frustrated with this brand new boat.

 

[steelespike]

Re: Tohatsu Nissan TLDI 50 hp prop selection

I looked on the allweld site.It appears the boat has 8 ridges like keels down the bottom .I wouldn't think that would help speed much.I did notice one picture empty boat and driver, motor seemed to be trimmed in/down close to all the way.It wouldn't hurt to check that the motor is tuned right and throttle opens all the way. You might have a tech use a shop tach to verify the tach is accurate. We've had a couple of times here with wrong tach and wrong setting.
I think I would start with basics.Empty the boat keep the tabs up all the way.
maybe the stock prop, I don't think the powertech is the prop for you, lower motor to antivent plate even with the bottom then checking trim and gradually raising to a ventilation point checking trim as you go.If a portable tank start with it in the stern and move it forward as required.More than likely your not going to be able to use full trim ever but you need to find a setting and weight placement where it can hold the boat at a reasonable angle.
If you don't want to go through all the playing around have the motor checked and try a 4 blade prop. Might help the porpoising. Should have good hole shot, stay on plane with reduced throttle
and handle better at speed and at the dock.Unfortunately it may cost some top end.
The Solas Amita has been predictable with good results.

 

[myhuntfish]

Re: Tohatsu Nissan TLDI 50 hp prop selection

I looked on the allweld site.It appears the boat has 8 ridges like keels down the bottom .I wouldn't think that would help speed much.I did notice one picture empty boat and driver, motor seemed to be trimmed in/down close to all the way.It wouldn't hurt to check that the motor is tuned right and throttle opens all the way. You might have a tech use a shop tach to verify the tach is accurate. We've had a couple of times here with wrong tach and wrong setting.
I think I would start with basics.Empty the boat keep the tabs up all the way.
maybe the stock prop, I don't think the powertech is the prop for you, lower motor to antivent plate even with the bottom then checking trim and gradually raising to a ventilation point checking trim as you go.If a portable tank start with it in the stern and move it forward as required.More than likely your not going to be able to use full trim ever but you need to find a setting and weight placement where it can hold the boat at a reasonable angle.
If you don't want to go through all the playing around have the motor checked and try a 4 blade prop. Might help the porpoising. Should have good hole shot, stay on plane with reduced throttle
and handle better at speed and at the dock.Unfortunately it may cost some top end.
The Solas Amita has been predictable with good results.

Thanks for your help. I have removed the jack plate because it just has not helped anything and causes the boat to sit lower in the back, which causes water to come over with waves and when stopping. i lowered the motor to the bottom hole, which puts the cav plate 1/4" above the bottom of the hull. I also tried another powertech prop, a NREB 10.5 X 12" pitch. It did perform better than any so far. My RPMs are at 5800 with just me and a light load. About 5500 with a heavy load. Still porpoises with no tabs. I did remove the smart tabs and bolted on some fixed tabs 8" wide that stick out 3" behind the hull even with the bottom. Still not ideal. It will run 35 mph with just me, and 32mph with 3 people with this set up. I am just not happy with this boat/motor. I am going to take it to the dealer for fist service and a full chech up.

 

[chris3298]

Re: Tohatsu Nissan TLDI 50 hp prop selection

Thanks for your help. I have removed the jack plate because it just has not helped anything and causes the boat to sit lower in the back, which causes water to come over with waves and when stopping. i lowered the motor to the bottom hole, which puts the cav plate 1/4" above the bottom of the hull. I also tried another powertech prop, a NREB 10.5 X 12" pitch. It did perform better than any so far. My RPMs are at 5800 with just me and a light load. About 5500 with a heavy load. Still porpoises with no tabs. I did remove the smart tabs and bolted on some fixed tabs 8" wide that stick out 3" behind the hull even with the bottom. Still not ideal. It will run 35 mph with just me, and 32mph with 3 people with this set up. I am just not happy with this boat/motor. I am going to take it to the dealer for fist service and a full chech up.

I have pretty much the same boat as you, it's a week old 2011 15x52 V LA alweld 17 inch transom 2011 Tohatsu 50TLDI short shaft. I had me and my dad in the boat with motor all the way down on transom and motor tilted all the way down and at WOT there was no porpoising hen started to trim the motor up it started to porpoise. The Carolina skiff J-14 and same motor porpoised so bad it wanted to buck you out the boat. I just raised the motor to the 3 hole and am gonna run it by myself tomorrow. I'd like more speed out of it, I'll bring the gps along and see what it runs, I should have done this when the motor was completely down i hope i don't have a porpoise problem raising it so high.

Anyway just curious to know how you like your setup so far have you been able to work the bugs out? I know you're pain about the porposing that J`14 I had I sold it because it had two rockers and a bad hook in it, it was messed up from the factory that was by far the worst boat I have ever owned I really hope this alweld is better and so far I think it will be.

I know this is an old thread but really curious to know how your setup is now.

Thanks
Chris

 

[steelespike]

Re: Tohatsu Nissan TLDI 50 hp prop selection

Your really better off just posting your own question.
Using the only numbers he gave with any real value and guessing at other values
the calculator I use with 1.85 ratio, 12% slip (high end of normal) with a 15" prop at 35 mph the motor was only turning about 5100 rpm motor is rated at about 5700.Its unhealthy to run so low. As I posted all those keels aren't likely to make for a speedy boat .And the Jon boat form doesn't have much sofistication for speed.If you can tame the porpoising your better off with that than a boat that wants to lay downn flat all the time.
Usually the higher the motor is the less chance to porpois and less resistance through the water.Unfortunately without rpm figures speed doesn't mean much.
I would think 35 on a boat like yours is reasonable and the likelyhood of speeds
close to 40 unlikely.

 

[myhuntfish]

Re: Tohatsu Nissan TLDI 50 hp prop selection

I have pretty much the same boat as you, it's a week old 2011 15x52 V LA alweld 17 inch transom 2011 Tohatsu 50TLDI short shaft. I had me and my dad in the boat with motor all the way down on transom and motor tilted all the way down and at WOT there was no porpoising hen started to trim the motor up it started to porpoise. The Carolina skiff J-14 and same motor porpoised so bad it wanted to buck you out the boat. I just raised the motor to the 3 hole and am gonna run it by myself tomorrow. I'd like more speed out of it, I'll bring the gps along and see what it runs, I should have done this when the motor was completely down i hope i don't have a porpoise problem raising it so high.

Anyway just curious to know how you like your setup so far have you been able to work the bugs out? I know you're pain about the porposing that J`14 I had I sold it because it had two rockers and a bad hook in it, it was messed up from the factory that was by far the worst boat I have ever owned I really hope this alweld is better and so far I think it will be.

I know this is an old thread but really curious to know how your setup is now.

Thanks
Chris

Chris,
I have really not used the boat much since my last post. Really got burnt out on fishing (and dealing with problems with the new boat setup)about July and started getting into deer hunting mode. I have stayed with the NREB prop in 10.5 X 12 as it gave the best overall performance. My boat is the exact same boat and motor as yours. I have added aluminum flooring to mine so its a little heavier. I plan to check into some more props- most likely a 4 blade soon. I will tell you that if I had it to do over, I would definately get a longer flat bottom boat. My boat porpoises so bad it is unuseable without the smart tabs if I trim up at all. If I dont trim up, it plows and has terrible motor torque. The tabs are OK and do solve the problem, but they spray water everywhere. I wish I could tell you I love the boat, but I don't. It is a nice setup and I have enjoyed it so far, but I really expected better performance out of the 50hp and definately did not expect the boat to porpoise like it does. I really hope yours does not have these problems. If I can help you let me know. Ed

 

[chris3298]

Re: Tohatsu Nissan TLDI 50 hp prop selection

Thats really sad to hear, with my motor all the way down and my dad who weighs 250 sitting on the deck forward it never porpoised until I started to trim the motor up.
I just took it out today with the motor raised up two bolt holes on the transom and it porpoised like crazy. I then decided to take the advice of someone over on the boatracingfacts.com forum which was to lower the motor all the way down on the transom and this boat has trim tabs welded to the hull, to adjust them you have to bend them down. Mine must have been bent during shipping of the boat so I bent them down to being level with the bottom or maybe slightly below level and am gonna go run the boat tomorrow and see what happens. I was told to to keep bending those trim tabs down till you are able to trim the motor up level then after you achieve this then you can go up with the motor for more speed.

The carolina skiff J 14 I had taught me a lot, it had two rockers and a bad hook. The only thing to do was sand the bottom and build it so it would be flat and I said forget it and sold it and took a loss. I was really kinda diapointed with the alweld for when I put a straight edge under the boat it had a hook it in and was totally flat between the chimes but still better then the skiff. I did say though when I bought this boat if it didn't work for me I'm going full custom build or I may build the dam thing myself, no less then 3/16 aluminum on bottom for sure.

The good thing though is the metal is thin enough you could pound it out with a dead blow if needed. I'm a out of work welder and I can say to weld aluminum this thin and keeping it not from warping is tuff and I must say quality of the welds are pretty dam good to.

I agree I do need to somehow put a tack on this motor and see what my rpm's are.

You really may want to go over to the boatracingfacts forum those guys are hardcore racers and hillbilly backwoods river racing people who know there stuff. I've learned alot about boats from over there. If it makes you feel any better you are better off with this boat then a Carolina skiff.
I was gonna go fishing tomorrow but think I'm gonna go test this boat out in the river and see how it runs, if it's useless then who knows i maybe putting 250 pounds of weight at the bow to make it run good.

Put a straight edge under that hull and see what it looks like.

I could start another thread and maybe will but it is nice to find someone with similar setup.

Chris

 

[chris3298]

Re: Tohatsu Nissan TLDI 50 hp prop selection

dang thing wouldn't let me edit, i guess I type to much.

Wanted to add the prop guy near me told me on my last boat that a prop will NOT stop porpoising so you gotta put a straight edge under that hull and see if it's flat.

 

[myhuntfish]

Re: Tohatsu Nissan TLDI 50 hp prop selection

Chris,
I hear you, but man this seems like deja vu. I have done everything you speak of. I checked the bottom of the boat before I did anything- I am an ex sheet metal fabricator/welder. Like yours, my boat is definately a quality built boat. Welds look great, but it does have a slight hook. My boat also had the welded on tabs- which in my opinion are a band aid fix. They will stop the porpoising, but in my case they had to be bent down below the bottom of the boat slightly, which creates drag, reduces top speed and sprays water back on me and the motor. I moved the motor up, down, added jack plate and moved it up/down again. No better and actually worse in some cases. I spent hours on the boat racing facts site. I am local to the guys you speak of. I even spoke to "50hptiller" on the phone. Like you said, these guys are very knowledgable, but I do not want to race my boat. The advise I got was to remove all the weight in the front, even the trolling motor and get a jack plate & a "merc Chopper prop". Don't get me wrong, I would love to go faster, but not that way. I just want my boat to run about 38-40 with no porpoising. Take my advise, dont waste your time with a jack plate- it will not help and put stress on the transom. It also hangs the weight back and will cause water to come over the short transom every time you stop and the boat will float lower in back. I have my motor one hole up from being bottomed out on the transom. This puts the cav plate about 1.5 " above the keel- if my memory is correct. I havn't looked at it lately. I cut back the welded on tabs and left just enough to bolt the hinges of the smart tabs to. This was so I did not have to drill through the transom. The smart tabs will totally fix your problems. Probably the single best thing i have done. I really do not like that I had to install smart tabs to make the boat usable, but I have found no other fix. In my opinion, the boat is just too short for a motor this heavy. I think if it were 17' or even 16' instead of 15', we would not be having the porpoising problem. Still, I do plan to try a 4 blade prop and may look into pontoons as well. I may also look into mounting a permanant style fuel tank in the front seat.

Ed

 

[steelespike]

Re: Tohatsu Nissan TLDI 50 hp prop selection

It does appear these boats have a design flaw probably too much rocker.
If it has a hook it would tend to lay down but might porpois when trimmed up because the hook is fighting the bow lift. Problem with any tabs is they create drag and it sounds like yours are really dragging.
Your smart tabs may have been too small.Probably rated for your size boat but you have
problems that act like that of a bigger boat.
You might try welding on an "afterplane" Extend the bottom about 5 or 6 inches beyond the transom I've seen racing outboards with them.(not adjustable)You may have to include adjusters to fine tune the angle.Adjust so it barely removes the porpoising problem.
Your 35mph is certainly reasonable. My 50 Evinrude on my 375lb big Crestliner bare bones utility only calculates to about 38 with a 2.42 ratio and a 19" prop.at 5500 rpm.
Unfortunately I haven't ever clocked it.

 

[chris3298]

Re: Tohatsu Nissan TLDI 50 hp prop selection

This really stinks I'm gonna go try my boat now in the river and se what it does, dam I sure hope I don't have a porpoising problem riding by myself because i'm tired of wasting money on boats that don't perform. You know to have a boat perform you might just have to go all totally flat bottom because I had bought that 25 yamaha for the skiff and first off put it on my 12ft flat bottom riveted boat and it had no problem with porpoising. AHHHH this makes me sick to my stomach hearing this. Well I always wanted to build my own boat I maybe getting that chance real soon because I can't see paying someone to build a boat and screw it up.

Steelespike I have seen what you're talking about, what I've seen was a extra 4 to 6 inches but it was across the entire back of the boat and I was kinda thinking the same would this help

 

[myhuntfish]

Re: Tohatsu Nissan TLDI 50 hp prop selection

I feel your pain. I really think it is mainly the weight issue in the back. I had a 1448 semi v Sea Ark with a 30hp johnson tiller. I never had a single problem with porpoising like with this boat. But you have to consider- the 30 johnson weighed about 115lbs, no battery (manual rope start), 6 gal tank and me (150lbs then) in back, troll motor and battery in front. This boat- 50 TLDI - 210lbs, 100lb battery, fuel filter assembly & guage pod with tack- 10 lbs, 6 gal tank and me (uh- now about 180lbs- Im eating good), troll motor and battery in front. So I have a little bigger boat that is only 1 foot longer with about 250 more pounds in back (extra motor weight, battery, guages/fuel filter & 30 more lbs of redneck) and a lot more horspower for leverage. As stated I think this is the problem. The way I see it you have a few options with this boat. 1. Move as much weight from the back to the front as possible- battery, fuel tank. 2. Put smart tabs on and deal with the spraying water and drag. 3. Try the afterplane or pontoons. Other than that I see no solution becasue the boat is just too short.

 

[steelespike]

Re: Tohatsu Nissan TLDI 50 hp prop selection

Exactly; all the way across with a notch to clear the lower unit.
Actually it was on a wood Reveau racing boat from the 1950s.I think it assisted getting on plane and perhaps kept it from bounding around.If I recall right I think it blended into the sides a little,probably to keep it from catching in a turn.

 

[chris3298]

Re: Tohatsu Nissan TLDI 50 hp prop selection

Just back from the river, first thing i noticed is well i may have bent those trim tabs a little to much past the level part of the bottom and noticed more spray. Well the thing got on a plane quick and the nose was down was thinking dam maybe i bent them to much, ran WOT and was thinking dam my fat dad in the front it seemed faster then i forgot to trim the motor up I did with just very small burst of the button ran like that a while till I got use to it. I then said ok time to trim and get this motor level and well it was tuff to tell I think I was pretty close to being level meaning triming the motor up. I wish I would have brought a tape measure to then measure the bottom of the tiller handle to the seat and make this measurement again when on dry land to see just how level the motor was and forgot the dam gps. I felt like i was a lot faster triming it up, there was times that it was porpoising but was able to get on the throttle and work the porpoise out. Today was very windy and not a good day for fishing but barely good enough for testing the boat on the river.

Something I noticed was when trimmed up and wot it didn't feel like much of the boat was running in the water, at times the wind or current seem to catch the boat and want to move me over, it felt like, the back end was very loose meaning felt like not much was in the water but felt dam fast. Almost like it was easier to move the tiller but at the same time very easy to get out of control.



My friend has a custom flat bottom boat he had made down here in Louisiana and it has 3/16 bottom and 1/8 side heavy but a tank and can run over anything. He has the extended piece of aluminum acting as a trim tab but cut out for the lower unit and makes me really wonder how much that help. I think his extended out maybe 2-3 inches possibly

So that is where i'm at now I'm kinda tempted to maybe bend those tabs a spec more but hell as of right now if felt dam fast and nothing like that worthless carolina skiff I had.

I should add my fat a** weighs about 235

 

[myhuntfish]

Re: Tohatsu Nissan TLDI 50 hp prop selection

Just back from the river, first thing i noticed is well i may have bent those trim tabs a little to much past the level part of the bottom and noticed more spray. Well the thing got on a plane quick and the nose was down was thinking dam maybe i bent them to much, ran WOT and was thinking dam my fat dad in the front it seemed faster then i forgot to trim the motor up I did with just very small burst of the button ran like that a while till I got use to it. I then said ok time to trim and get this motor level and well it was tuff to tell I think I was pretty close to being level meaning triming the motor up. I wish I would have brought a tape measure to then measure the bottom of the tiller handle to the seat and make this measurement again when on dry land to see just how level the motor was and forgot the dam gps. I felt like i was a lot faster triming it up, there was times that it was porpoising but was able to get on the throttle and work the porpoise out. Today was very windy and not a good day for fishing but barely good enough for testing the boat on the river.

Something I noticed was when trimmed up and wot it didn't feel like much of the boat was running in the water, at times the wind or current seem to catch the boat and want to move me over, it felt like, the back end was very loose meaning felt like not much was in the water but felt dam fast. Almost like it was easier to move the tiller but at the same time very easy to get out of control.



My friend has a custom flat bottom boat he had made down here in Louisiana and it has 3/16 bottom and 1/8 side heavy but a tank and can run over anything. He has the extended piece of aluminum acting as a trim tab but cut out for the lower unit and makes me really wonder how much that help. I think his extended out maybe 2-3 inches possibly

So that is where i'm at now I'm kinda tempted to maybe bend those tabs a spec more but hell as of right now if felt dam fast and nothing like that worthless carolina skiff I had.

I should add my fat a** weighs about 235

what prop are you running?

 

[myhuntfish]

Re: Tohatsu Nissan TLDI 50 hp prop selection

Chris,
to make sure the motor is level or perpendicularl- level the boat while on the trailer using the trailer jack, then put a level on the motor cavitation plate and use the power trim to level the motor. When all is good and level, take a paint marker and mark the transom bracket in the front where the motor pivots or hinges on both halves of the bracket. Then when you are running, you know when these two marks are lined up the motor is at even trim.

 

[chris3298]

Re: Tohatsu Nissan TLDI 50 hp prop selection

I'm using the stock aluminum prop that came with the motor which it says 11.1x14 I believe.

Good idea about the paint marker I never really thought about that, I'll try this tomorrow if it isn't to windy and hopefully will remember that dam gps. Really seemed like a difference in speed when I was able to trim it up and boy did it feel LOOSE and FAST but never know really till what that GPS reads. I just have a gps for a car but should tell me my mph still. I did notice less spray though from the trim tabs when I was able to trim it up a little.

Previous reply you said you have aluminum plate in the floor to make it level, you know you can add Marine plywood to your floor it is probably lighter and I tell you that stuff will last about 30 years or longer if you paint it. The transom on my 12ft my dad gave to me when I was 16 is made out of that stuff and it's probably about 16 years old or older now and been out in the weather all these years. That really is some dam good stuff and if you search it isn't priced to high. Here it is about 65-85 for a 4x8-1/2 inch sheet.

I'm gonna go out in my garage now and go level that motor off so I don't forget about it.

I must add though I did notice when take off maybe I got on it to much but that dam bow comes up kinda high then back down and takes off like a bullet first couple of times scared me but then it was down right FUN. Another thing I noticed at one point it was kinda hoping at WOT and by sliding my fat butt just a couple inches forward I was able to get it to level out. I must say I learned alot about this boat today and way less worrying or frustration compared to that dam skiff.

I started thinking about what you said about the boat needs to be long and it won't porpoise, I kinda thought the same but to be honest there are guys who have souped up 40's on 13-14ft aluminum flat bottom boats that don't porpoise at high speeds. I'm starting to think that maybe having this slight hook isn't a great thing either like I think steelepike said. I mean it's better then having the two rockers and a bad hook like I had with the skiff but I'm thinking on a flat bottom square nose boat when there built it is easier to probably build it and not get the hook that maybe the V's have. Maybe by building it as a V there's of course more welding distortion making the different parts forcing them together creating a hook maybe more. I don't know it's kinda theory I'm kinda having. I guess I'll let you know someday if this is true for when I attempt to build my own aluminum boat. This one will be built for redneck speed.

Chris