Interesting issue after transom replacement?

[Traxion]

I have ran into an interesting issue after the transom replacement on my Sea Nymph SS175. The motor and all associated items were put on exactly as they were. However, performance is completely different. My prop that I had been running now acts completely different. The only thing I can figure out is with the badly rotted transom, my trim angles were different than they are now with the new transom. There was definitely some sag and flex in the rotten transom, but I never imagined it being as drastic as it is. Honestly, it acts like I raised the motor and went up two inches of pitch on the prop. Anyone else ever run into this?

 

[Friscoboater]

Re: Interesting issue after transom replacement?

Just a guess, but could it be because the weight is different? Lighter, heavier?

 

[Traxion]

Re: Interesting issue after transom replacement?

I don't know that there is or was enough of a weight change to make any difference. Nothing really changed there. Everything went back exactly as it was. Only thing that could be different is foam and buoyancy, not exactly how it was but very close. Buoyancy shouldn't affect performance, at least in this case.

 

[ljc1957]

Re: Interesting issue after transom replacement?

Find a "before" picture of the boat and compare where it sits in the water compared to your new transom. Hope that makes sense.

 

[drewpster]

Re: Interesting issue after transom replacement?

I agree with you that the thrust angles are going to be very different. Also its more likely that the boat is lighter, not heavier. If it was holding water it was holding weight that you removed. Its been my experience that lighter boats ride a little rougher and feel a little squirrelly. The trim tab under the cav. plate will make a bigger difference than you may think. Make some adjustments and see what happens. I am doing the same thing today with my tri-hull. It has allot more horse power than the original setup. It wants to kick to starboard on hard acceleration. My trim tab is set to starboard. I'm going to try it a little to port and do some test runs. I let you know if it has an effect.

 

[Traxion]

Re: Interesting issue after transom replacement?

Although I have no ideas on what my fully trimmed down or trimmed up angles are, I do know that I probably had almost 3/8" of sag/additional negative trim with the rotted transom. I'm going to punch the angles in and figure things out exactly, maybe that sag is more appreciable than I am guessing. However, it just seems to be such a major difference I am having a tough time wrapping my head around it. It acts like I am 2" too big on pitch and the motor is up too high. Drastic to say the least, my initial thoughts to get it back to where it was is going down in pitch and go from there.

 

[Cadwelder]

Re: Interesting issue after transom replacement?

I have ran into an interesting issue after the transom replacement on my Sea Nymph SS175. The motor and all associated items were put on exactly as they were. However, performance is completely different. My prop that I had been running now acts completely different. The only thing I can figure out is with the badly rotted transom, my trim angles were different than they are now with the new transom. There was definitely some sag and flex in the rotten transom, but I never imagined it being as drastic as it is. Honestly, it acts like I raised the motor and went up two inches of pitch on the prop. Anyone else ever run into this?

What you're experiencing isn't unusual. I've seen it it several of my restores.

#1. Although you may not think so you're boat is a good bit lighter. (I've lighten them by as much as 300 pounds due to water soaked wood and foam)

#2. Now with a solid transom your trim angle isn't different it's just stable therefore performance will improve.

#3. The last boat I restored was an 18' with a 150 Merc. after the restore I had to go to 2" higher pitch prop to keep the rpm's down in range (lighter boat)

Sounds like you did a good job to me.

 

[Traxion]

Re: Interesting issue after transom replacement?

I get what everyone is saying, however the boat acts like it got heavier not lighter. I mean, I am running the boat loaded as I have for several years and the difference is just drastic. Way less overall grip with the prop, porpising, and blowout and pretty low trim angles compared to where I used to run the motor. Just a puzzling deal.

 

[joebob14]

Re: Interesting issue after transom replacement?

Like cadwelder said it sounds like you did it right and have lessened the weight in the rear of the boat. loaded just like it always has been means the front of the boat sits where it used to and the rear is floating higher, almost like pointing the front of the boat down towards the water more. I would try to maybe move some of your weight towards the rear of the boat and if that dosnt work you could try one of those wwail tail things that mounts to your cavitation plate. I have one on my boat and it helps the prop bite alot better.

 

[drewpster]

Re: Interesting issue after transom replacement?

Does your mount have any stops in place, or is it trimmed down as far as it can go?

I understand your logic but it seems to me the engine will push out from under a lighter boat easier than it will a heavier one. A heavy boat will take more push to get it going, but it will remain more stable while doing so. See my meaning?

Seems to me you need to trim down more.

BTW- I can also see why a whale tail (mounts to cav. plate) would seem like a good idea. I don't recommend them. I have removed several, and done better without them. They may have thier place, but they tend to throw in an added factor that is usually worse than better. I have not had much luck with them.

 

[Cadwelder]

Re: Interesting issue after transom replacement?

I get what everyone is saying, however the boat acts like it got heavier not lighter. I mean, I am running the boat loaded as I have for several years and the difference is just drastic. Way less overall grip with the prop, porpising, and blowout and pretty low trim angles compared to where I used to run the motor. Just a puzzling deal.

Porpising is a concern....my very first restore had that problem...come to find out I glassed a twist into the hull from not supporting it properly during the restoration, it's very easy to do. This is why I stress proper support of hulls since they get really flimsy with all the decks and stringers removed.

Try doing a visual inspection from the front of the boat sight down the center line and from side to side and see if there is any twist in the boat??

How did you maintain it's shape during your restore??

 

[Traxion]

Re: Interesting issue after transom replacement?

The hull is aluminum, only thing that was taken out was the transom, decks etc stayed in place. Nothing moved, I am 100% certain of that.

Motor currently has a stabilizer on it (SE300). I've ran it with and without and with the props I have been using it was better with it on. It was on before the transom replacement and is on there now.

Motor has low end stops for the trim. I can't recall exact position but it's definitely not fully down. But, by the "feel" of the boat, I really don't need anymore negative trim. Fully trimmed down now, holeshot is OK and you quickly have to trim up get the weight off the front of the boat once on plane to accelerate.

I've done the math and a 1/2" sag at the pivot point of the motor only equates to around 2 degrees of negative trim. I don't know the entire range of the motors trim in degrees, maybe 2 degrees is substantial.

As far as weight in the boat, I can't get any more in back. I've got the big motor, 8 hp 4s Kicker, batteries, oil tank, everything in there. Fuel tank is mounted in the floor 1/3 from the back. Livewells are up front but they were empty. Gear goes in the back too. Boat is definitely weighted more from centerline back.