Another new start for Helmsman

[Helmsman]

Thanks Nick. Helpful

What i didn’t say before was somewhere above the 8’s I see material bow rise. Leading to the question.

Tabs left flat would have some impact too compare to none installed. Seems to me.

I have a 480hp. The trim tabs help anywhere over about 10 mph. I haven’t actively measured the fuel reduction, but have noted that it reduces fuel usage. If I remember correctly, Scott recommended tabs for boats higher than the 380 hp engine. I agree with FWT’s philosophy of keeping the boat as simple as is practical. At least I believe it was him who stated that before in other posts.

 

[FWT]

I have a 480hp. The trim tabs help anywhere over about 10 mph. I haven’t actively measured the fuel reduction, but have noted that it reduces fuel usage. If I remember correctly, Scott recommended tabs for boats higher than the 380 hp engine. I agree with FWT’s philosophy of keeping the boat as simple as is practical. At least I believe it was him who stated that before in other posts.

Thanks

Yes, I made the KISS argument before.

And yes, when I ordered and had a conversation with Scott about engine size, it was said 380hp and 10 knots was about the inflection point. From everything I've seen myself or from responses to my question, that seems to be spot on.

Still happy with my decisions: 380hp, with a normal speed of 7-8 knots. But reserve power I hope to never "need".

The hull performs beautifully for my intended use

 

[Helmsman]

Thanks

Yes, I made the KISS argument before.

And yes, when I ordered and had a conversation with Scott about engine size, it was said 380hp and 10 knots was about the inflection point. From everything I've seen myself or from responses to my question, that seems to be spot on.

Still happy with my decisions: 380hp, with a normal speed of 7-8 knots. But reserve power I hope to never "need".

The hull performs beautifully for my intended use

If I were making the decision today, I would probably go with the 380. My wife was pretty insistent on the 480, with a concern about outrunning weather. We rarely use the extra power, though it came in handy when passing a barge in a wider part of the river last year which saved us about ten miles of 5-6 mph and a two hour wait at the lock.

 

[MYTraveler]

Although not directly applicable, here is my experience with trim tabs on big boats. My semi-custom boat, which is about 60' LWL, displaces abut 100,000 pounds and tops out at about 18 knots, comes with trim tabs as standard equipment. Even though the tabs are large, I was skeptical that they would be of any practical value. And my experience with my 12 prior boats is that they are often a maintenance nightmare. So, I opted to omit the tabs, expecting some modest credit against the purchase price to reflect the saved labor and equipment. Instead, I was told that since the molds were configured for tabs (the tabs fully retract into the hull), omitting them was actually more labor and exceeded the equipment cost savings. The builder graciously called it even.
In any event, I haven't missed having tabs. The bow rise is so slight, all the way through the speed range, including as it comes up on plane, as to be not noticeable. The Helman's are not quite as big, but I suspect the limited benefit of tabs would be similar. But confirm with a sea trial, if possible.

 

[rslifkin]

Although not directly applicable, here is my experience with trim tabs on big boats. My semi-custom boat, which is about 60' LWL, displaces abut 100,000 pounds and tops out at about 18 knots, comes with trim tabs as standard equipment. Even though the tabs are large, I was skeptical that they would be of any practical value. And my experience with my 12 prior boats is that they are often a maintenance nightmare. So, I opted to omit the tabs, expecting some modest credit against the purchase price to reflect the saved labor and equipment. Instead, I was told that since the molds were configured for tabs (the tabs fully retract into the hull), omitting them was actually more labor and exceeded the equipment cost savings. The builder graciously called it even.

Usefullness of tabs depends a lot on the hull design. Some boats really only need them for some trim adjustment on plane, some just get on plane a little faster with them, but then others are designed to rely heavily on the lift from the tabs for planing.

Maintenance wise, I'm not a fan of tabs that retract under the hull. It's a great spot to get growth that causes problems.

 

[MYTraveler]

Maintenance wise, I'm not a fan of tabs that retract under the hull. It's a great spot to get growth that causes problems.

As is often observed, boats are a series of compromises. My boat is optimized for long range fishing. One aspect of that is the elimination of protrusions from the stern that could snag a fishing line -- hence tabs that fold up into the hull, rather than the more common approach of extending from the stern. In a further effort to enhance fishability, the hull extends all the way to the rear of the swim platform so that the swim platform is not cantalievered. Not only does that further reduce snag risks, but the area under the swim platform serves as two gigantic fish holds, the starboard one of which is insulated and is fed by the ide chipper. So, we typically put freshly caught fish into the port-side hold to bleed out, and then transfer to the starboard side to get rapidly cooled down.

If not for the fishing focus, and particularly if the boat were a bit smaller, if I were opting for tabs, I would probably have them mounted to extend from the hull, not only for maintenance considerations, but also because from what I have seen the stern lift is enhanced, and probably contributes to increased efficiency as the boat approaches planning speeds.

 

[Nick14]

Thanks Nick. Helpful

What i didn’t say before was somewhere above the 8’s I see material bow rise. Leading to the question.

Tabs left flat would have some impact too compare to none installed. Seems to me.

Experience with the 38 Sedan may not be directly applicable to the 38E. My understanding is the Sedan is about 1,000 lighter than the Pilothouse, with the extra weight of the Pilothouse carried aft with the heavier rear cabin structure. It makes sense you would see stern squat/bow rise before the Sedan.

Your bow rise above 8 knots makes sense. The hull speed of the boat is around 8 knots (6 x 1.34). Anything above that starts interfering with those pesky laws of hydrodynamics. Beyond hull speed means stern squat, bow rise, bow wave, etc.

If WOT is 10 knots I don't know if tabs would help much. The force exerted on the tabs at 8-10 knots could be calculated and guesstimate if it would raise the stern/drop the bow by an appreciable amount, though 10 knots wouldn't be fast enough to lift the boat onto a semi-planing attitude. In the 9-10 knot range the trim tabs on my boat add about 0.5 knots of speed at a given rpm, and do noticeably (though not massively) add trim down at the bow, though my bow rise at 10 knots is not major.

The only way to know would be to try.

 

[FWT]

Experience with the 38 Sedan may not be directly applicable to the 38E. My understanding is the Sedan is about 1,000 lighter than the Pilothouse, with the extra weight of the Pilothouse carried aft with the heavier rear cabin structure. It makes sense you would see stern squat/bow rise before the Sedan.

Your bow rise above 8 knots makes sense. The hull speed of the boat is around 8 knots (6 x 1.34). Anything above that starts interfering with those pesky laws of hydrodynamics. Beyond hull speed means stern squat, bow rise, bow wave, etc.

If WOT is 10 knots I don't know if tabs would help much. The force exerted on the tabs at 8-10 knots could be calculated and guesstimate if it would raise the stern/drop the bow by an appreciable amount, though 10 knots wouldn't be fast enough to lift the boat onto a semi-planing attitude. In the 9-10 knot range the trim tabs on my boat add about 0.5 knots of speed at a given rpm, and do noticeably (though not massively) add trim down at the bow, though my bow rise at 10 knots is not major.

The only way to know would be to try.

Nick

Thanks for that.

I have been zeroing in on my opinion of the sweet spot, at 1700 RPM doing 7.7 knots.

With my first cup of coffee this morning it occurred to me that’s close to hull speed, and indeed made the calculation and it is. So it all makes sense.

 

[rslifkin]

Nick

Thanks for that.

I have been zeroing in on my opinion of the sweet spot, at 1700 RPM doing 7.7 knots.

With my first cup of coffee this morning it occurred to me that’s close to hull speed, and indeed made the calculation and it is. So it all makes sense.

Efficiency wise the sweet spot will be slower than hull speed, probably no more than 7 kts. 7 kts will likely burn significantly less than 7.7, but slowing down further will show smaller gains.